The Unseen World

1980s, Boston

First, it was late August and David was hosting one of his dinners. “Look at the light, Ada,” he said to her, as she stood in the kitchen. The light that day was the color of honey or of a roan horse, any warm organic thing like that, coming through the leaves of the tree outside the window in handsome dapples, lighting parts of the countertop generously, leaving others blue.

David said to her, “Please tell me who explained the color of that light.”

“Grassmann,” she said.

And he said, “Please tell me who first described refraction.”

“Snell.”

“Before Snell.”

It was a name she couldn’t remember, and she placed a hand on the counter next to her, unsteadily.

“Ibn Sahl,” he said to her. “It was the genius Ibn Sahl.”

David was fond of light in all its forms, fond of recalling the laws of optics that govern it. He had a summer cold that day, and from time to time he paused to blow his nose, gesticulating between each exhalation to make some further point. He was wearing his most comfortable shirt, wearing old leather sandals that he had bought for himself in Italy, and his toes in the sandals flexed and contracted with the music he had chosen — Brendel, playing Schubert — and his knees weakened at each decrescendo and straightened at long rests. In the blue pot was a roux that he was stirring mightily. In the black pot were three lobsters that had already turned red. He had stroked their backs before the plunge; he had told her that it calmed them. “But they still feel pain, of course,” he said. “I’m sorry to tell you.” Now he took the lobsters out of the pot, operating the tongs with his right hand, continuing to stir the roux with his left, and it was too hot for all of this, late summer in an old Victorian in Dorchester. No air-conditioning. One fan. Windows open to the still air outside.

This was how Ada Sibelius liked her father: giddy with anticipation, planning and executing some long-awaited event, preparing for a dinner over which he was presiding. David was only selectively social, preferring the company of old friends over new ones, sometimes acting in ways that might be interpreted as brusque or rude; but on occasion he made up his mind to throw a party, and then he took his role as host quite seriously, turning for the evening into a ringmaster, a toastmaster, a mayor.

That day was such an occasion, and David was deep into his preparations. He was director of a computer science laboratory at the Boston Institute of Technology, called the Bit, or the Byte if he was feeling funny. And each year in August, he invited a group of his colleagues to a welcome dinner in honor of the new graduate students who annually came through the lab. Ada knew her father’s peers nearly as well as she knew him, and in a way they also felt to her like parents: alongside David, they had raised her, whether or not they realized it. She was, in theory, homeschooled, but in fact she had been lab-schooled, spending each day at her father’s work, putting in the same hours he and his colleagues did. At night he rounded out parts of her education that he felt he hadn’t adequately addressed: he taught her French, and gave her literature to read, and narrated the historical movements he deemed most significant, using Hegelian dialectic as a theoretical framework. She had no tests, only spontaneous oral quizzes, the kind he was giving her now while he stirred and stirred the roux.

“Where did we leave off,” he asked Ada, “with Feynman diagrams?” And when she told him he asked her to please illustrate what she had said on the chalkboard hanging on the kitchen wall, with a piece of chalk so new that it stuttered painfully over the slate.

He looked at her work over his shoulder. “Correct,” he said, and that was all he usually said, except when he said, Wrong.

All afternoon he had been chattering to her about his latest crop of grad students. These ones were named Edith, Joonseong, and Giordi; and Ada — who had not yet met them — pictured them respectively as prim, Southern, and slightly inept, because she had misheard Joonseong as Junesong and Giordi as Jordy, a nickname for a pop star, not a scientist.

“They were very good in their interviews,” said her father. “Joonseong will probably be strongest,” he said.

That night Ada was in charge of the cocktails, and she had been instructed on how to make them with chemist-like precision. First, she lined up eight ice-filled highball glasses and six limes on a tray with a lobster pattern on it, which her father had bought for these occasions, to match the lobster he would be serving for the meal. Into the frosted highball glasses she poured sixty milliliters of gin. She cut the six limes in half and flicked out their exposed seeds with the point of the knife and then squeezed each lime completely into each glass. She placed two tablespoons of granulated sugar into the bottom of each and stirred. And then she filled each glass up with club soda, and added a sprig of mint. And she put a straw in each, too, circling the glass twice with it, giving the liquid a final twirl.

It was 6:59 when she finished and their guests were due at 7:00.

The lobsters were cooked and camping under two large overturned mixing bowls on the counter, so they would stay just slightly warmer than the room — the temperature at which David preferred to serve them. Her father had made his cream sauce and was assembling the salad he had dreamed up of endive and grapefruit and avocado. He was moving frantically now and she knew that talking to him would be a mistake. His hands were trembling slightly as he worked. He wanted it all to be simultaneously precise and beautiful. He wanted it all to work.

“What am I forgetting,” he said to Ada tensely.

Lately she had noticed a change in her father’s disposition, from blithe and curious to concerned and withdrawn. For most of her life, Ada’s father had been better at talking than at listening, but not when it came to her lessons. When it came to her lessons, to the responses she gave, he was rapt. When it came to some other, lesser topic of conversation, he drifted from time to time, looking out the window, or at what he was working on, giving birth to moments of silence that lasted longer than she thought possible and ending only when she said, “David?”

Where he had formerly sat and chatted with her or furthered her lessons until it was time for bed, now he went into his home office and worked on his computer, sometimes staying up until the early hours of the morning, sometimes falling asleep at his desk and hurrying to work with a spiderweb of red lines upon his face from whatever had creased it overnight. Sometimes she woke to find him writing at the kitchen table, filling yellow notepads with unknowable screeds, blinking at her with a certain lack of recognition when she wandered into his orbit. Sometimes he went off on walks without telling her, returning hours later with little explanation. Sometimes she woke to find him puttering around the house in odd attire: his swim trunks or his one suit jacket, a wrench or hammer in his hand, fixing things that he never before had seemed to notice. He had always kept a workbench and a sort of makeshift laboratory in a room off the basement — it was where he had taught her chemistry, with various substances he borrowed from friends at the Bit or extracted from household products or from nature — but he spent more time there now, building devices in glass and plastic that looked meaningless to Ada. They looked like goggles, or helmets, or masks. She had donned several of them, when her father was out, and found them heavy and useless; she could not see out of them, though they bore openings over each eye. “What are they?” she asked him, and he had only told her they were part of a new project.

He still ate dinner with her each night but recently had seemed abstracted, or in a fog: she tried to engage him with questions about history or physics or mathematics, but the answers he gave were short ones, not the usual lengthy monologues he formerly delivered with such gusto, and these days he never asked her questions afterward to make sure that she had understood. But her lessons were still regular enough, and interesting, and with very little effort Ada could easily persuade herself that he was fine. She told herself that he must be working on something quite important, something he didn’t yet feel ready to share with anyone, even her. Convincing herself of this was in every way an act of self-preservation, because her world revolved entirely around her father, and any disturbance in this orbit threatened to send her spinning into space.

“Cheese and crackers,” David said. “Of course.”

Ada ran to get them, but the kitchen was disastrous by then and she overturned one of the gin rickeys in the process. It leaked onto the lobster tray and down the side of her leg.

“Shit,” she said, too quietly to be heard. She had recently learned to curse: it was her one act of rebellion against her father, who was not prudish but thought that cursing was uncreative, in some way unintelligent.

She mopped up the liquid with a rag and got out the cheese and crackers and put them on a wooden cutting board—“Put some of the mustard in the center,” said her father; “Not like that, like this”—and then, as she was making a new drink, the doorbell rang. It was a four-part chime that David had rigged himself, the first four notes of Beethoven’s Fifth — which themselves were, he had explained to her, meant to sound like death or fate, some powerful perennial force, rapping at the door. Her father sprinted out of the kitchen and into the main room to let in his first guest, and from the kitchen she heard that it was Liston: the low confident voice, the local accent that enthralled her, that she imitated in private, that she and her father did not have.

“Come in, come in,” said David, “come in, my Liston.”

Liston had a first name: it was Diana, but for as long as Ada had known her she had been only Liston to David, and therefore she was Liston to Ada, too. Liston, his best friend, his best thinker, first author on all of his papers; Liston, their neighbor, who lived four houses away from them. It was Liston who convinced David to move to this neighborhood shortly after Ada’s birth: a studio apartment in the Theater District would not work for a father and daughter, she had told him, once the daughter was over the age of four. So Liston’s friend Connie Reardon, the real estate kingpin of Dorchester, had found David this house on this street, Shawmut Way, and Liston had approved, and began calling him “neighbor” for laughs.

Liston was very smart and impressively self-educated: David had said once that she was raised on the wrong side of the bridge in Savin Hill by a plumber and a homemaker, on the middle floor of a triple-decker, and Ada had asked him what it meant to be from the wrong side of the bridge, and he said it was poorer over there, and then she asked him what a homemaker was, and he told her it was a woman who does nothing but raise her children and keep her husband happy and her house tidy. “Very unlike Liston,” he had stated approvingly.

Liston was Ada’s favorite person in the world aside from David. She gathered scraps of information about Liston’s life as if assembling a quilt: Liston no longer had a husband. She had an older daughter, Joanie, twenty-six and out of the house now, and three younger sons. David had briefly recounted the story of Liston’s divorce: she married too young, at eighteen, because Joanie was on the way. It was to a boy from her neighborhood, he told Ada, someone who did not understand the scope of her talent and the particular requirements of her career. (Ada had vague memories of this husband, who was still married to Liston for the first five years of Ada’s life: she remembered a large, unpleasant figure who never made a noise, except to exhale occasionally after something Liston said.) After Joanie was born, Liston worked her way through UMass as an undergraduate and then, after several professors there noticed her outstanding scientific and mathematical mind, she earned her doctorate in electrical engineering from Brown. David hired her as a postdoc, and later full-time. Liston divorced her husband right after the birth of her son Matty, four years younger than Ada, and since that time had relied on a large network of the women friends she grew up with for child care and emotional support. In the words of David, the husband was no longer in the picture, and good riddance. “This must be the most important factor in your choice of a life partner,” he told Ada. “Who will most patiently and enthusiastically support your ambitions?”

“Shouldn’t she have recess, or something?” Liston once asked David, several years before, when she noticed Ada becoming pale from spending every day inside the lab. “Agreed,” said David, and so every day at lunch he had begun to march her around the Fens for thirty minutes, observing the flora, naming the birds by their songs, pointing out where Fibonacci sequences occurred in nature, once finding a mushroom that he said was edible and then cooking it up for the lab. Sometimes Liston joined them, and when she did it was a special treat: she derailed David’s monologues at times; she told Ada about her childhood; she told Ada about the music that her three sons listened to, and the television shows they watched, and at night Ada wrote down what she had heard in her journal for future reference, in the unlikely event that she was ever called upon to discuss popular culture with one of her peers. Often, Ada felt as if Liston were teaching her some new language. She consumed greedily everything that Liston told her. She looked at her with wide fixated eyes.

Now, entering their house, Liston said, “My God, David, it’s hot,” except her accent made it sound like hut. Of Liston’s many verbal particularities, Ada’s favorites were as follows: bahth, Liston said, for bath; and hoss for horse; and she used various expressions passed down to her by her mother that Ada rolled around in her head like marbles. “He’s been in and out like a fiddlah’s elbow,” she’d said once about David, who had a habit of letting his office door slam, not out of anger but out of forgetfulness.

Solemnly Ada brought a drink to her and Liston thanked her and called her her favorite girl, and she asked Ada to tell her why it was that her sons weren’t so polite, asked her to please explain what was wrong with them. David retreated to the kitchen to keep things in order and then the doorbell went again, and this time it was Liston who opened it.

The man on the porch was wearing leather driving shoes and fitted red shorts the color of the cooked lobsters and a white button-down linen shirt that looked cool despite its long sleeves, which he had rolled up to his elbows. He was impressively tan. Dark hair coated his calves and rose up from the top button of his shirt and rose thickly back, in waves, from his noble brow.

“Are you Ada?” he asked her, after greeting Liston, and she added another accent to her mental list of sounds to ponder and reproduce. She nodded.

“A pleshure. I’m Giordi,” he said, and introduced himself by kissing her one time on each cheek. Ada was used to this exchange from interactions with her father’s many European colleagues, and from the many graduate students who had come to the Bit from other parts of the world; but it never failed to fluster her and to make her feel impossibly self-conscious, aware of her physical self in a way she did not like to be. There was the feeling always that she should be prettier than she was. That she should be better dressed, more put together. Like Giordi. Like some of the other members of the lab, Charles-Robert, Hayato. Unlike Liston, who dyed her hair a tinny red and sometimes wore clothes that were too young for her, and unlike David, who prided himself on caring more about almost everything than clothing. Food, yes; science, yes; Ada, yes; clothing, no. And he expected this of Ada also — that she would rank her wants in the same order he ranked his own. The wants she did not tell him about (cable television, Nancy Drew books, a waterfall of bangs like Liston’s, a hair accessory called a banana clip that looked something like a foothold trap) felt to Ada shameful and perverse. They felt to her ignoble.

“Would you like a drink?” she asked Giordi, as she had been taught, and then she led him down the hallway toward the kitchen, where David greeted him. Giordi took the gin rickey in his hands, putting his lips to the rim of the glass, ignoring the straw.

“Did you made these?” he asked Ada, about the drink, and she told him that she did, fixating on the grammatical mix-up he had let slip, pondering its structure.

“Delicious,” he said. “Wherever did you learn.”

“From my father,” she told him.

She had learned everything from her father.

Ada was twelve years old. She would have been in seventh grade that year, if she had been enrolled in a school. She had never kissed a boy, never held hands with a boy. Had never, in fact, intentionally been within the vicinity of a boy her own age for more than a few minutes. Nor a girl. Her only interaction with boys and girls her own age had been with the children of her father’s colleagues, who in general led more normal lives than she did—normalcy being a condition that her father disdained and she revered. And even these interactions had been cursory. Ada’s behavior around these children was absurd. When she got near them she drank them up. She took them in. She was silent. She watched them like a television show. She took note of every turn of phrase they used. Like, they said. Rad. Prolly. No way. As if. Freaky. Whatsername. Hang out. What’s up? Duh. Creep. Freaked out. They were freaked out by her, probably. She didn’t blame them.

Ada was much more accustomed to spending time with adults, and tonight she would have been very much at ease except that she could sense her father’s tension and it made her tense. He had always been a perfectionist when it came to his dinners, but tonight was extreme: he had been preparing for days, writing down lists, stopping at the store each evening for things he had forgotten. She could not articulate what was different in his demeanor, but it triggered a deep-seated uneasiness in her. It was a hair in her mouth or sand in her shoe. She looked at her father now: he was lifting up the mixing bowls to show Giordi the cooked lobsters on the countertops.

“Aragosta, sì?” asked her father, who prided himself on speaking enough of every language to get by in restaurants at the conferences he went to in Europe, in Asia.

But Giordi shook his head. “Those are astici,” he said. “Aragoste have the little things like. .” he said, and he mimed spikes. “And they don’t have the big. .” and he mimed claws, pinching his thumbs and his tightened fingers together.

“Astici,” said David, and Ada knew from his expression that he was attempting to file the word in a deep recess of his mind.

The other members of the lab arrived next, Hayato and Frank, and then Joonseong — whom she quickly realized was neither Southern nor female — and Edith — whom she quickly realized was not prim, but young and pretty. The only missing member of the lab was Charles-Robert, whose daughter had a soccer game. Ada gave each of them drinks in the living room and watched everyone as they fell into patterns of conversation: Liston and Hayato, the fun ones, were huddled in a corner, laughing about something or someone at work; they’d continue to huddle until one or the other realized that they were hovering on the verge of rudeness, and then they would break into conversation with someone else. Edith and Joonseong were speaking with Frank, who was much more polite than the rest of the group, engaging them in various lines of inquiry about their background and their families and their home countries and their accommodations in Boston.

Ada hovered in the background until Liston noticed her and waved her over, and she put a strong and steady arm around her, brought her in close to her side, and squeezed.

“Good drinks, kiddo,” said Liston. Ada sank into her side, grateful for something she couldn’t articulate.

At 8:00, Ada’s job was to ask all the guests, politely, to be seated for the meal.

The night before, David had made place cards: before she’d gone to bed she’d seen him fashioning them with index cards and a ballpoint pen, sitting at the kitchen table, the tip of his tongue just visible between his lips. Now they were assembled on the rectangular table. Ada, sitting between Edith and Joonseong, wished that she had been seated next to Liston, her favorite, or Giordi, whom she had decided was quite handsome — but she knew that one of the things that David expected of her was that she would help him to entertain his guests. She took this role seriously, and, in preparation for the night, had dreamed up several topics of conversation that she felt ready to introduce if necessary, culled from the newspaper and from the books she was reading.

David was passionate about cooking — to him it was a cousin of chemistry — and the first course was chilled cucumber soup, made in a blender, thickened with cream, which she helped him to transport from the kitchen, careful not to spill. “A regular Julia Child,” said Liston. Ada brought cold white wine to the table and poured it neatly into every glass, including a splash into her own: since she turned twelve, David had been allowing her a quarter of a glass on special occasions. The several sips of wine she was allotted made her feel warm and capable, made her feel as if there were real possibilities before her in the universe, that they were hers for the taking.

Next were the lobsters, but before they were brought out David smacked his head and returned to the kitchen.

“I almost forgot,” he said, and reemerged with a bundle of plastic in his hands. On his face was a look of almost exquisite lack of self-awareness — he was so pleased with himself, so pleased with life in that moment. He raised his eyebrows in glee.

“Oh, here they come,” Liston said. They were the lobster bibs that David had gotten from Legal Sea Foods, years ago, at a dinner out with his colleagues. Putting them on was the traditional rite of passage for all the new grad students at David’s annual feast: he delighted in these sorts of place-specific rituals, reveled in the New England-ness of it all, took pleasure in his longtime residency in the region (and in seditiously dismissing his own past as a New Yorker), wished to bestow this piece of local color on every visitor who passed over his threshold. The bibs were five years old by then and badly tattered, but over and over again David trotted them out for dinners with new friends, because they said LOBSTAH on them in a Gothic script, and he thought this was a funny joke, and was quite proud of them.

He passed them out one at a time to every guest.

“And you wear this for all dinner?” asked Giordi, incredulously, and David nodded.

“It gets quite messy,” he told Giordi. “You’ll be grateful later on.”

Now David brought the lobsters out, two at a time, carrying them in his hands, and he examined every one, looked it in its lobster face and declared which guest would consume it. “You look like a lobster for Frank,” he said to the largest, “and you for Ada,” he said to the smallest. There was cold potato salad on the table, and cold asparagus, and little pots of drawn butter and lemon that David had positioned precisely in front of every guest, and three ramekins of cream sauce that were meant to be shared. There were tomatoes that David had picked from his garden, festooned with mozzarella and basil.

David raised his glass once the lobsters were distributed. “To our new graduate students,” he said. “Welcome to Boston.”

“The home of the bean and the cod,” said Edith.

“And the lobster,” said Hayato.

Sufficient alcohol had been consumed; there were no uneasy pauses, no long breaks in conversation that required Ada to bring forth one of her prepared talking points. Instead, she sat next to Edith and took in her outfit. She was even more beautiful than Ada had initially realized, and a sort of smooth-skinned glowing ease emanated from her person, into the thrall of which Ada imagined men fell powerfully. Edith was fashionable and reserved: Ada noticed with some jealousy that one of the banana clips she coveted pulled Edith’s hair away from her face loosely, giving her a look of orchestrated carelessness. She wore a sleeveless, collared floral dress with a knee-length hemline and buttons done up to her neck. She did not carry a purse but there were large pockets on the dress, and Ada wondered what she kept in them: A pen, maybe. Lipstick, maybe: her lips were a light unnatural pink, a radioactive color that David probably did not like. A lighter, Ada thought. She could have been a smoker; many of David’s European colleagues were. She was remarkably pretty.

Edith turned, caught Ada observing her, smiled.

“How old are you, Ada?” she asked: the first question new adults usually asked.

“Twelve,” Ada said, and Edith nodded sagely.

“And what are your favorite books?”

“The Lord of the Rings books,” Ada said, “are my favorite books of all time.”

In fact they were her father’s favorite books of all time, but she had adopted them as her own so fully that she was no longer certain what the truth was.

Edith studied her for a moment. “Twelve,” she said. “A difficult age for me. Better for you, I’m sure.”

Was it? Ada looked around the table at her father and her friends. They were her constant source of companionship, of knowledge, of camaraderie; each one offered to her some necessary part of her existence: Frank for kindness, and Liston for protection and love and common sense, and Hayato for artistry and humor. And the others, who could not make it: Charles-Robert for confidence and a sort of half-serious disdain for outsiders; Martha, the young secretary of the division, for knowledge of popular culture and fashion. And, above all others, David, for devotion and knowledge and loyalty and trust, David as the protector and guide of them all. But despite the completeness of what the adults around her offered to Ada, the sense of reassurance and comfort they extended, something was missing from her brief existence, and she knew, though she could not bring herself to fully form the thought, that it was friends her own age.

The dinner moved through salad and into dessert — Giordi had playfully kept his bib on well beyond the lobster course, insisting that he could not be trusted without one and that he would wear one regularly now — and Ada leapt up several times to refill the wine glasses of the guests. A fast-moving storm had swept through the neighborhood, and the house was finally cooling off. A damp breeze came in through the windows. They were near enough to the ocean to smell it, on nights like these. David invited everyone into the living room, and Ada stayed behind to clear the table.

When she had finished, she joined the group, and found that the guests had arranged themselves into little clusters. She hesitated for a while on the threshold of the living room, wiping her hands on the back of her shirt, and then joined Frank and Joonseong. In moments when it seemed appropriate, she produced some of the topics she had earlier bookmarked for discussion — a recent shooting in Mattapan; a French film from the 1950s that David had taken her to see at the Brattle; the restaurants surrounding the Bit, and their strengths and weaknesses — but she found herself increasingly distracted by David, who was standing slightly apart from any group, gazing at the floor. He had his hands clasped behind his back; he looked vaguely, unsettlingly lost. Ada nodded and feigned attentiveness as Joonseong told her about his new apartment, but in her peripheral vision she saw David walking slowly toward the window, as if lured there by a spell: he stood still then, and she saw his lips moving quickly, his hands hanging stiffly by his sides.

“David,” said Liston, who was closest to him. “Are you all right?” Ada saw her say it. And at this he lifted his head quickly, and smiled, and turned and clapped his hands once. Everyone looked at him.

“A riddle,” David announced, “for the newest members of the lab. And the first to solve it gets a prize.”

Ada heard a thickness in his voice that she didn’t recognize. She would have thought he was drunk, except that he rarely drank: a glass or two of wine was all he ever took, and tonight he’d barely had any at all. Together, everyone watched him.

This was his ritual: to each new crop of grad students, he delivered the same riddle, one he adored for its simplicity and the justice of its logic. All the permanent members of the lab could recite it and its answer in unison: they had all heard it so many times. Still, it comforted Ada somehow to hear him deliver it each year, as if it were scripture — to watch the same looks of thoughtfulness pass over the faces of the grad students, and then a lighting-up when one of them came upon the answer.

Everyone watched David expectantly: classmates observing a teacher. He cleared his throat and began. “You are a traveler who has come to a fork in the road between two villages,” he said. “The village of West is full of only murderous men incapable of telling the truth; visiting it will bring about your death. The village of East is full of benevolent men incapable of lying; visiting it will bring to you a cache of gold. Two men stand in the fork in the road — one from West and one from East. But you don’t know which is which. In order to determine how to reach the village full of gold, and avoid your certain doom, you may ask only one question of only one man. What should your question be?”

The grad students paused. One of them would ask David to repeat the problem: it happened every year. This year was Joonseong, and most likely it was due to his English, not to his logical abilities. David incanted the riddle once again, repeating it word for word. Edith was smiling about something Ada couldn’t determine, and at the end of David’s second recitation she put a hand out before her to signal that she had an announcement.

“I’m recusing myself. I know the answer because I’ve heard the puzzle before. I cannot tell a lie,” she said.

“I suppose that makes me an Easterner,” she added, and Giordi laughed too eagerly, or perhaps he was simply grateful to have understood her joke.

David then turned to Giordi and Joonseong, with some seriousness, and informed them that it was between the two of them, and reminded them of the prize. Both of them looked down at the floor contemplatively. Ada’s money was on Joonseong, from the way her father had described both men. But there was a silence over the room that went on for quite some time, and eventually both of them looked at one another and then at David. Joonseong raised his hands in surrender.

David looked pleased.

“Giving up, are you?” he asked them, giddily. “Even you, Giordi?” If David’s first love was being stumped, his second was stumping others.

David opened his mouth. Then he closed it.

“Your question must be,” David said. “Your question,” he said again.

He folded one arm about himself and put the other hand to his cheek. Everyone watched him. A slow unfurling sense of panic filled the room.

“My word,” said David, slowly. “I seem to have forgotten the answer.”

This was a moment that became sealed forever in Ada’s memory, encased in glass, a display in the museum of David’s decline. She never forgot the brief silence that followed, during which everyone looked down at the floor and then up again, or the way that Giordi loudly cleared his throat. Or the way that David looked at her, almost in horror: the look of a pilot who has just discovered that the engines of his plane have failed. The humiliation Ada felt on his behalf was almost too much to bear. At last, she let herself articulate in her mind the thought that she had been repressing for a year or more: that something was wrong with David.

“Oh, you know it, David,” Liston finally said. “My God, of course you do.” She looked around at the rest of the group entreatingly. “The traveler would point to either of the villagers and ask the other one, ‘Which way would he tell me to go to get to the cache of gold?’ And either man would say, ‘East.’ ”

David nodded. “Yes.”

“The liar would say that the truth-teller would say East, because he only lies. The truth-teller would say that the liar would say East, because he knows that the liar always lies. East either way,” said Liston.

“And so you would go to the village of West,” said Liston. “And find the cache of gold. And then you’d take your friend Liston out for a nice steak dinner.”

“Yes,” said David. “Quite right. You’re quite right, Liston.”

There was still too much silence in the room. David looked lost, the smile gone from his face, staring at the wall opposite him as if looking into the future.

Ada wondered if this was a moment that she should fill with conversation.

“Today is the one-hundredth anniversary of the disastrous eruption of the volcano Krakatoa,” she said. It was one of the news items that she had culled from the paper.

“Oh, really?” said Edith. “I hadn’t heard.”

“Of course,” David said. “What would he say?”

“You knew it,” said Liston.

“I knew it,” said David, pensively.

“I suppose this means you win the prize, Liston,” he added, and then he walked out of the room.

Frank murmured something about it being late. Hayato announced that he’d give the grad students a ride home.

And Ada stood frozen in the living room, not knowing what to say.

Liston squeezed her shoulders and went to the kitchen to say goodbye to David and then, from the front hallway, called out, “Good night, Ada, see you on Monday!”

“Good night,” Ada said quietly. She did not know whether Liston heard her.

She heard the sound of the front door opening and closing, and then the thunder of six pairs of feet going down the old wooden stairs of the porch, punctuated by a quick, indecipherable interjection from a male voice.

For a moment the house was quiet. And then she heard the front door open once more. David cried out, “Liston! Your prize!”

From the living room, Ada peered out into the hallway to see the back of her father. He was standing with a hand on the open door, his head bowed. In the other hand he held a little golden bag of chocolates he had bought the day before at Phillips’s. Liston was out of earshot, probably already walking up the steps to her porch. The taillights of Hayato’s car went past the house and were gone. After a few moments David closed the door, and Ada disappeared before he could turn and see her.

She washed the dishes. For twenty minutes, she let the warm water run over her hands.

Finally, she went to the dining room to retrieve the tablecloth and there was David, sitting at the long dining room table, turning over and over in his hands a sort of worry stone, a lucky charm in the shape of a clover. He kept it in his pocket wherever he went. He said it helped him to think. He looked vague and puzzled.

He shifted his gaze toward her. She was angry with him for reasons she knew were unjust. She had never before seen his mind fail him so resoundingly. It threatened to rattle her long-standing impression of him as someone stately, noble, just.

“Sit down,” he told her.

She paused.

“Just for a moment,” he said. “Please.”

She complied, and he rose and walked into his office, which opened off the dining room. It was one of the only places in the house that Ada avoided: the desk was mired completely in piles of papers; the built-in bookshelves were filled entirely, and stacks of books had begun to take over the floor. She saw the back of him as he bent to open one of the drawers of the desk, and from it he produced what he was looking for, and turned and carried it back with him. He sat down across from her once more.

“Here,” he said. Ada looked at it. It was a floppy disk, and on the hard cover of it, a white plastic clamshell, he had written, For Ada. She opened it. On the label affixed to the disk itself, there was a message: Dear Ada, it said. A puzzle for you. With my love, your father, David Sibelius.

“It’s a present,” he said. “Something I’ve been working on.”

“What is it?” she asked him.

“You’ll see,” he said. “You’ll see when you open it.”

Ada was born in 1971 to a woman whom David had hired as a surrogate. At the time this was nearly unheard-of, but — as David described it — when the opportunity arose, he took it. The surrogate was a hippie-ish woman named Birdie Auerbach, and Ada had had no contact with her since, though at the time of her birth Birdie had made it clear to David, and David had subsequently made it clear to Ada, that she could if she wanted to. But throughout Ada’s childhood she had felt she really didn’t need to; she felt that somehow it would be a betrayal to David if she did.

Ada never questioned his decision to bring a child into the world; her connection to him was so complete that it felt entirely natural to her. She imagined that he simply decided he wanted a child and then had one. David had never had a romance in Ada’s lifetime, not that she was aware of. He was devoted to his friends and colleagues and to various people whom he occasionally mentored: there had been a number of grad students over the years, and the piano tuner, and the landscaper who mowed the lawn, whom he often invited inside for lemonade and quizzed about his business plans. There was a young girl who lived down the street who showed promise as a ballet dancer, and he encouraged her mother, with whom he had developed a friendship, to bring her to audition at the School of American Ballet in New York City — the only place, he assured her, that one could really get a proper education in dance in the United States. He spent long hours talking with Anna Holmes, the librarian at the nearest branch of the Boston Public Library, about her life and her hobbies and her interests. She was pretty, unmarried at fifty, and could possibly, Ada thought, be in love with David. He had taken an interest in her, and in all of these acquaintances, but though he discussed them with Ada frequently and exhaustively — speculating about their friendships, their home lives, their careers — it seemed clear to her that his interest in Miss Holmes was platonic, though Ada would not even have thought to articulate it as such. He never discussed his romantic history overtly with anyone, as far as she knew. It would have seemed to him undignified. Ada had heard only vaguely about former girlfriends, young debutantes he had known when he was growing up as part of New York’s upper class. She had always slept soundly, but she had some vague memories of hearing a female voice in the living room, though she also could have been dreaming. Ada supposed it was possible that on those occasions her father could have been entertaining a guest. He would never, ever have talked to her about it. The idea would have been repugnant to him: he had always been private about his personal life to an extreme, even with Ada, despite the fact that he regularly assured her of her great importance to him and of the fact that he thought of her as his closest companion.

David was forty-six when Ada was born and had already been head of his own lab for sixteen years. For the first years of her life — when she was too young to entertain herself for long days at work — Ada had a nanny, Luda, a tall, soft-spoken Russian woman with one long braid down her back, whom David hired to watch her while he was out. But at night and on the weekends it was David and Ada alone. The fact that she survived her infancy astounded her sometimes. She couldn’t imagine it, though she often tried: David, waking up in the night to attend to her, warming bottles, boiling them; or preventing her from falling off of anything high or running into anything low or being bitten by anything mean; or taking her to the park in a stroller; or folding her snugly into a blanket; or gazing down at her while she ate from a bottle; or letting her fall asleep on his fatherly chest: these actions seemed so incongruous with Ada’s idea of David as to be impossible. And yet he must have done these things: she was alive as the proof.

Ada’s memories of David began later, with their conversations. She could not remember not talking to David. Every waking hour was, in his mind, an opportunity for interesting conversation, a chance to analyze their lives and the lives of all humans. “Are we very happy, Ada?” he often asked her, and she always said yes, though sometimes with hesitation — as if she knew that the question itself implied the opposite. But for the most part, she was utterly content with her strange, satisfying existence: Ada and David together, always.

He had small rituals: he made tea in an elaborate old-fashioned way that, he said, his mother taught him; and he watched a certain police drama religiously, the only television show he enjoyed, often shouting out the perpetrator’s name halfway through the episode, crowing each time he was correct; and when Ada was small, before bedtime he would read to her from books that he loved, never children’s books; and on Sunday afternoons he liked to go to a particular café in Dorchester to organize his brain. Ada did whatever homework he had assigned her while he wrote out formulas and drew diagrams, in his cramped particular handwriting, on stacks of napkins provided to him by Tran, the eponymous owner of the café, who was himself an amateur scientist, well versed in Feynman and Planck. Her father, though a computer scientist by profession, had a strong background in pure mathematics. He was interested in all the sciences, and in the humanities as well: he had learned French as a boy and still spoke it fairly well, and from time to time would attempt to teach himself something like Mandarin or Portuguese. “A well-rounded thinker should be able to puzzle out from scratch any proof that has ever been proven,” he said to Ada, and so sometimes to keep sharp he would work out some problem of physics or mathematics, although it had nothing to do with his research. When he was working on these, or on any puzzle, he would fall into a trance familiar to his closest associates — in which his body seemed utterly, utterly at the will of his mind — in which his hands, writing furiously, seemed overtaken by a ghost. He was expressionless, an automaton, and could not be spoken to until he returned. On the occasions when, in one of these trances, he worked himself to sleep, Ada put a hand on his shoulder — one of the few times she ever touched her father — and he sat up and blinked, disoriented, until he realized where he was.

Her father spoke of his past only rarely, but occasionally he would agree to tell Ada the tale of his life as a story before bed. She begged him to: it was a way of expanding her family, a way to counteract the feeling she sometimes had that the two of them were stranded on an island. To comfort herself, Ada sometimes narrated his life in her head, using the wording he would have used.

David was born in New York City, he told her, the only child of wealthy parents to whom he would eventually stop speaking. They died before Ada was born. He described them with bitterness and scorn, ridiculing their conventionality, their closed-mindedness, their snobbery. (Ada did not point out to her father, though it occurred to her, that many of his opinions could be labeled snobbery as well; and that his last name, well known in the Northeast, had opened various doors for him that he seemed not to notice.) The rift between David and his parents, which led at last to a complete estrangement by his late twenties, was caused by differences of opinion regarding how he should live his life—the phrase he always used. He hinted vaguely at their displeasure at his choice of career, his refusal to accept their introductions to the various young ladies they would have liked to see him marry, his refusal to obey the conventions and codes that accompanied the family’s status. “Debutantes and that sort of thing,” said David. “Charity balls. Teas.” At the mention of these terms he would shudder, which signified an end to the story. Ada rarely pressed him beyond this point.

The derisive, sardonic tone he used when speaking of his past implied he had long ago moved on, had long ago dismissed those families and their ilk as fraudulent and obsolete. From his scraps of description Ada gathered that his mother and father were stern and impersonal. Worse than that, she categorized them as uncreative — David’s term, one he used only for those he held in complete disdain. His father had been a sort of gentleman attorney, one who only took on clients who were personal friends, and only then if he could be sure the work would end amicably. His mother had no career aside from identifying and articulating the flaws of her husband and son. Every conversation with her, he told Ada, was like a game of chess: one had to remain several steps ahead of her to ward off whatever criticism would be imparted if one’s guard was let down.

In these moments Ada was jolted by a sudden vision of David as a child, subservient to his parents, not the master and commander of everything around him, as she’d thought of him for most of her childhood. It was difficult to picture.

This much she knew: David was raised on Gramercy Park in a grand and beautiful row home, up which ivy spread densely and then in rivulets, like fingers from a palm. She saw it once a year, in winter, when David took her for a weekend trip to New York City for Calvary Episcopal’s annual Christmas concert. It was his childhood church — the only site from his childhood that he ever wished to revisit — and it was his favorite sort of music: early choral composition by Tallis and Purcell. He was not churchgoing, but it was liturgical music that moved him the most, and he sat very still and upright in the old wooden pew for the duration of every song, his head bowed as if in prayer. Only his fingers moved from time to time, playing his knees like an organ.

Afterward David would walk swiftly out the door, and Ada would run to keep pace with him — difficult to do, for he walked as if he were skating, with a lengthy, forceful stride — and turn left toward Gramercy Park, and then stand silently with Ada outside of the house for several seconds. They never spoke. Usually the heavy drapes inside the house were drawn by the time the concert let out, but once Ada saw a young girl, about her age, sitting with her mother at a dining room table. “I wonder if those are Ellises,” said David idly, naming the family who purchased the home after the death of his parents. “I read about them in the paper. I’ve never met them.

“I would have been the only heir,” he told Ada. “I wouldn’t have taken it anyway,” he added, and then he walked quickly down the street, without warning her, so that she had to run for several steps to catch him.

Despite his complete dismissal of his past, he kept one black-and-white portrait of himself with his parents in the dresser in his bedroom. Ada had discovered it when she was quite young and often returned to it whenever he was out. There he was, young David, perhaps eleven years old. In the picture he was wearing a bow tie, a tweed jacket with a high waist, short pants, knee socks. A very slight smile played upon his mouth — same mouth, same lively light eyes. His parents looked predictably dour and serious: mother in a black scoop-necked satin dress that ended just above her ankles, black stockings and black shoes, a long black beaded necklace. Father in a dark suit and tie, one leg crossed over the other. All three of them were positioned slightly apart from one another. In the background was a funny scene: draperies, slightly askew, framed a fuzzy, impressionist backdrop of trees and mountains.

Their next-door neighbor on Shawmut Way was an old woman named Mrs. O’Keeffe, who had come over from Ireland at ten years old, in 1910. She had worked as a maid in the same neighborhood David had grown up in, and then she met her husband and moved to Boston. This coincidence came up early in their acquaintance, and Ada watched David as he physically cringed. Discussions about his past were always an encumbrance to him, but from then on he had difficulty dodging Mrs. O’Keeffe, who wished frequently to reminisce with him about the other families who had occupied those homes. She had not known him but she had known his people. She would name the families of Gramercy Park as if counting her treasures. “And the Cromwells,” she would say, “what a beauty their daughter was. And those Byrons, and those Harts, and those Carringtons. .”

“Yes,” David would say, “I knew all of them, once.”

He graduated high school in 1943, right in the middle of the Second World War, which normally would have guaranteed a period of service. But David was, even at that age, nearsighted to the point of legal blindness without his glasses. Instead, therefore, he went to college. He chose Caltech — which further horrified his father, who had gone to Harvard, and his mother, who saw it as a vocational school, a school for the working class. There he majored in mathematics. He then found his way to the Bit, where he received a doctorate in applied mathematics, and where his work on GOPAC, an early computer system spearheaded by Maurice Steiner, earned him such quick fame in his field that he was given his own lab at the Bit by President Pearse at the age of thirty. It was named for Steiner, after his death, and with David at the helm, it quickly became known in the field. It was here in 1970 that he met Liston, then a young postdoc straight from her doctoral work at Brown, and here that they became friends. They were an odd pair: he was sixteen years her senior, but she was an old soul — both of them said it — with two children already and two more to follow. They spent a great deal of time together both in the lab and outside it. He fostered her already considerable talent, and spoke of her proudly as her role at the lab expanded. “The best pure thinker in the group,” he said of her often, including himself in the tally. At this time, Charles-Robert and Hayato had already been hired, and Frank came shortly thereafter. A rotating cast of postdocs, grad students, and short-lived hires came and went, but the five of them, plus Ada, were the core.

Ada loved the lab: it was a dark and cozy complex of offices housed within the Applied Mathematics Division of the Bit, which itself was housed within one of the Bit’s many Gothic buildings, and it felt more like a home than a workplace. For most of the fifties, sixties, and seventies, a mainframe computer dominated the largest room, toward the rear; by the late eighties it had become obsolete, but it remained in the lab as a sort of relic, a hulking, friendly dragon lying dormant in the back. The front of the lab was composed, with the exception of a larger conference room, of a warren of small rooms and offices, scattered with machines, some of which were perpetually stripped of their front panels, their innards revealed. Each office had been personalized over the years to reflect its owner. Hayato kept an easel in his, on which he sketched out problems and occasionally landscapes; and Charles-Robert had covered his walls entirely in maps; and Frank, the youngest, used to keep an elaborate network of hot plates and crock pots and electric kettles, on which he cooked surprisingly competent and complete meals for the whole department, until one day the building manager found him out and stopped him, citing fire department regulations. Liston’s office was sparse but for a record player on which she played albums by ABBA and U2 and the Police, and a beanbag chair in which Ada sometimes napped when she was smaller. David’s office consisted mainly of a collection of filing boxes that he added to yearly, too busy to go through them, too paranoid to dispose of their contents unexamined. The grad students worked part of the time across town at the Bit’s smaller campus in the Medical Area, and the other half in cubicles in the main room. Anyone else who came through the lab as a temporary or permanent hire was placed into one of the three empty offices that were otherwise used by David as schoolrooms for Ada.

Many of her early memories involved the floor of the lab, the feet and ankles of scientists all around her. When she was very young she was given antique models of elements to play with. She was given a kit of wooden parts to make up atoms. Hayato blew up latex gloves, stolen from the biology department, and made turkeys of them with a felt-tipped pen. She was not taught nursery rhymes about geese and kings but about molecules: Here lies dear old Harry, dead upon the floor. What he thought was H₂O was H₂SO₄. She was named the mascot of the Steiner Lab, and there was a photograph of her dressed as a punch card to prove it.

She attended most formal meetings that the Steiner Lab conducted and she attended informal meetings, too, ducking in and out of offices at will, sitting still at the round brown table in the main room when the lab had lunch all together. And listening — always listening.

The theory of language immersion posits that a language is best learned by placing the learner into what is in effect a natural habitat, or a simulated habitat that strives for authenticity. Thus a student of Spanish will learn best not when she is taught to conjugate verbs but when she is surrounded by useful Spanish — not when she is taught Spanish for its own sake, but when she is taught every other subject in Spanish, too. More by default than intent, Ada was thus immersed in mathematics, neurology, physics, philosophy, computer science. She did not begin with Lisp, but with compiler design. In her physics lessons at home with David, she did not begin with s = d/t, but with the Grand Unified Theory. For the first years of her life, she did not know what she was hearing. Listening to David and his colleagues was like listening to radio chatter in a different language. And then, without knowing it or taking note of it, she began to be able to follow their conversations. By ten she was able to be a sounding board for her father as he worked out his ideas — not resolving them or bettering them, necessarily, but posing questions to him that were reasonable, and occasionally jarring something loose in him. When this happened, he reported Ada’s concern or comment to the rest of the lab with some seriousness at the next lab meeting, and a slow glowing warmth spread throughout her, because she had made herself useful to the group, whom she thought of, always, as her peers.

“A good question, I think, Ada,” David would say, and the rest of them would nod in agreement, and the group would move forward as one.

This was what Ada pictured when she thought of her father, the vision of David that she harbored and kept safe throughout her life, the idea pinned permanently to the sleepiest part of her brain: it was her father in his laboratory, or at Tran’s Restaurant; or in the library of the institute that employed him; or, rarely, in a crowd of friends; or, regularly, at his desk, in his small absurd office in their home, contemplating a chessboard, his head as bald and round and sturdy as a pawn’s. His woolen socks with holes in them. His hands the steeple of a church. He was tall and thin and rigorous in his studies and in his life, and he was inventive, and he was very warm and betrayed no one ever, and in Ada’s mind he was ethical beyond compare, and he had a habit of rubbing his hands together quickly when he was delighted or moved, and he was quick and spry and gentle and able with his limbs and head. He was dexterous, and his fingernails were clean, and he was wise, and he was intent upon seeking out the best and most beautiful versions of pieces by Chopin, Schumann, Schubert, and Bach, and he knew excellent riddles, and his name was Dr. David Sibelius, and she never called him anything but David.

In the weeks and months that followed the dinner party, no one mentioned its strange end to Ada, her father’s sudden lapse, or asked her any questions about David’s increasingly odd behavior. Occasionally, at the lab, she felt as if she and David were being excluded from something: where formerly Liston or Charles-Robert would have welcomed her into any room — discussed the bugs in a particular program with her, put an arm about her shoulders — now there was often a feeling of conversations stopping when she rounded a corner. The new grad students found their way into the routine of the laboratory, and Ada kept a closer eye on her father, noting peculiarities in his speech or habits when they arose, attempting to classify them somehow.

In the evenings, she worked at the puzzle on the disk David had given her, marked For Ada on its case. It had turned out to be, when she’d inserted it into her computer and started it up, simply a text document with a short string of seemingly random letters.

DHARSNELXRHQHLTWJFOLKTWDURSZJZCMILWFTALVUHVZRDLDEYIXQ, it read.

David would not give her any clues. Together, they had been studying cryptography and cryptanalysis for the past several years — a hobby of David’s that, he said, came out of his days at Caltech, where his mentor had been a cryptanalyst during the war — and he told her this was her next assignment. “It may take you a while,” he admitted. “Don’t let it affect your other work, of course.”

While she worked, he worked: in his office, with the door now closed sometimes. She looked at the outside of it, vaguely hurt.

Then Christmas came, and with it the Christmas party that Ada always anticipated and dreaded in equal parts, for with it came outsiders.

David loved Christmas. In addition to their annual trip to New York, he insisted upon several other traditions, and balked at any suggestion of variance: after dinner on Thanksgiving he always put on the record player an album of the Trapp Family Singers performing Christmas songs from around the world, and he played this regularly until January 2, and then packed it away; then there was the Stringing of the Lights that occurred on the first Saturday of December, and which David executed with an efficiency that put the other fathers on the block to shame. In mid-December they cut down a Christmas tree at an orchard in the Berkshires, a daylong expedition that he put on the calendar with great seriousness on December 1; and after that they visited Cambridge, where Frank lived, to go with him to dinner at a local Chinese restaurant and then to Sanders Theatre to see the Christmas Revels — a sort of scholarly variety show of medieval Christmas pageantry, with a dose of druidism thrown in as well. Just the sort of thing that appealed to David and his cohort.

“Isn’t it cozy out,” David was fond of saying, on first snowfall. “Ada, come look.” And if she was asleep, he would wake her; and she would rise from her bed, sleepy-eyed, rubbing her face, and walk to the window of their drafty house, and together she and David would stand in silence, together in the night, looking out onto Shawmut Way through a frosty, rattling window, their breath obscuring it slowly.

The Christmas party was the culmination of all of these traditions, and perhaps David’s favorite tradition of all. He insisted, always, that a party was not complete without some entertainment, a game, an organized activity that required everyone’s participation. Some years it was a hired guitarist or a group of carolers; some years it was a juggler or a magician. (“What else is one supposed to do — just stand around and drink?” asked David, perplexed.) It was this philosophy that caused him to declaim the same riddle to the new graduate students at the dinner he held for them every year; and it was this philosophy that had caused him, that December, to write a Christmas play for every member of the lab to perform, in front of a small audience of colleagues from other departments, spouses and children of lab members, and staff and administrators from other parts of the university.

He had told none of them this in advance. Instead, at 9:00, tinging his glass with a finger, he asked for everyone’s attention, and directed them all to form a semicircle in the main room of the lab.

“Here we go,” said Hayato, good-naturedly.

“Except you, Hayato,” said David. “You come up here. And you, and you, and you,” he said, grabbing the rest of the lab. “And you,” he said, last, to Ada, who had been praying to be forgotten. Her face burned as she walked to the front of the room and stood with the rest of them. In front of her, she saw a blur of faces before looking quickly down at the floor.

David was holding, in his left hand, a stack of stapled pages, which he passed out to each of them with mock seriousness, a flourish for each one. His face was pink and excited; his thick glasses were slipping down on his nose.

He turned back to the audience. “A play!” he announced. “A Christmas play.”

Later, Ada would not remember its exact plot — something about a group of superhero nerds sent back in time to determine how to achieve a better lift-to-drag ratio for Santa’s sleigh. (Ada played a reindeer.) What she did remember: David’s happiness, his complete contentment at the execution of his plan, how carefree he looked; and the way he directed them all, like a conductor with a baton; and her own embarrassment, her burning face, her quiet, noncommittal line delivery; and, in the front row, the faces of the audience members, some of whom looked bemused, some of whom looked befuddled; and there, to the right, at the edge of the crowd, the face of William, Liston’s oldest son, who stared at all of them incredulously, his mouth slightly agape.

In March she turned thirteen.

“A teenager,” said David, shaking his head. “Hard to believe, isn’t it, Ada?”

She nodded.

“Would you like a cake? I suppose you should have something festive,” said David, but Ada said no.

Secretly, she had been wanting one, a candle to blow out, a wish to make. She had gotten only one present that year, from Liston, naturally: a hot-pink sweater with a purple zigzag pattern that Ada loved but felt too self-conscious to wear. David had not gotten her anything: she was not surprised, since he was both absentminded and vaguely opposed to consumerism. That year, however, she had been secretly hoping for something from him, which she only realized when nothing came. Some external signifier of what she thought was an important birthday. A piece of jewelry, maybe. An heirloom. Something timeless and important. She wished, too, as she had been doing with increasing frequency, that she and David could engage in some of the more typical conventions that accompanied occasions such as birthdays. A big party with friends, for example. A sleepover: she had never had a sleepover. She had no one to ask.

That evening, after a quiet dinner at home, the telephone rang, and David answered in his office.

“Yes?” he said, slowly, a note of surprise in his voice. It was nearly 11:00 at night. Normally Ada would have been in bed, but she felt unsettled and alight with something: the newness of being a teenager, perhaps. She felt untired and alert.

From the dining room, Ada listened to her father, in his office, on the phone; but David was quiet for some time. She could see the back of him, the receiver pressed to his ear. He said nothing.

Abruptly, he stood and walked to his office. She caught his eye quickly, and then he closed the door. Lately he had been intentionally excluding her from things, and each time she felt the sting of it sharply.

She sat for a while at the dining room table, but, although she could hear the low murmur of David’s voice through the door, his words were indecipherable. She stood up.

She walked outside, into the sloping backyard behind the house on Shawmut Way. All of the yards on their side of the road were fenceless and connected, lined at the bottom of a small hill by a street-length row of trees. Dorchester was a city neighborhood comprised of other neighborhoods, mainly working-class, high in crime by the 1980s, appealing to David in part because of these features, because of his self-identification as somebody unassuming and down-to-earth. But the neighborhood they lived in, Savin Hill, was an old and Irish one, very safe, suburban in its aspect. Over a bridge that separated their part of Savin Hill from the rest of the city, two leafy roads formed an interior and exterior circle at the base of the hill the area was named for. Shawmut Way connected the two roads together, like a spoke in a wheel. A small beach spanned the eastern border of the neighborhood and a park with public tennis courts framed the central hill. Liston continued to live there because of these features and David had agreed to live there, against his normal preferences, despite them. “I feel like I’m on vacation,” he said, often, when walking home from the T after work. This was, from David, a complaint. He preferred that his cities feel like cities; but his respect for Liston’s advice, when it came to Ada’s needs, outweighed his resistance.

In the cool hour before midnight she walked down to the base of their backyard, to where the pine trees lived, and she ran her hand along their branches to find her way, quietly, through the three backyards between theirs and Liston’s. Lately, Ada had been doing this regularly, perhaps once a week, while David was working at night. He had never pressed her for her whereabouts — or maybe he had not noticed. If he had, he approved, because he liked to foster independence in her, liked to imagine that his daughter could take care of herself. Certainly he did not know what drove Ada to conduct these nighttime walks, these missions, these compulsive marches in the dark. Certainly he would have been surprised to learn that it was William Liston, fifteen, the oldest of Diana Liston’s sons. Certainly he did not know that Ada believed she was in love with him.

Since the Christmas party three months prior, Ada had thought about him almost unflaggingly, with a dedication singular to thirteen-year-old girls. For the first time, she also thought about herself, and her appearance. She stood in front of the mirrored vanity that David once told her had belonged to his mother, and she tilted her head first one way and then the other. Was she pretty? She could not say, and it had never before occurred to her to wonder. She was brown-haired and round-faced, with serious dark circles under her eyes and the beginning of several pimples on her chin. She had a widow’s peak that David told her he had had, too, when he had any hair to speak of. Like David, too, she wore glasses, which she had never before minded, but which now seemed like an unfair handicap.

She fantasized often about what she would say, what she would do, the next time she was in the same room with William Liston — though this rarely happened. Although Diana Liston regularly came over to their house for dinner when asked, the offer was rarely reciprocated; and although Ada saw her regularly at the lab, her three sons never came with her. Instead they lived what Ada considered to be normal lives: they attended a normal school, excelled or failed at various normal things like sports and English class. They had no cause to visit their mother at work, except when required. Therefore, the only time Ada found herself face-to-face with William Liston — or, truly, anyone her age — was at lab parties.

There were two reasons she felt ashamed of her crush: the first was that her father would have thought it was ridiculous — Ada knew that she was certainly too young, in his mind, to be interested in boys — and the second was that William was Liston’s son, and in a strange way she felt it was a betrayal of Liston to worship so ardently the child she complained about at lunch. “So listen to William’s latest,” she often said to Hayato, in front of Ada, and then proceeded to detail his most recent bout of mischief and the subsequent discipline he had received at school. Often it was for cutting class or leaving early; once, for forging a note from Liston excusing him from some assignment or other. He was caught by the number of misspellings he had included in the text. At the end of each account, Liston sighed and looked at Ada, mystified, and said, “Why couldn’t I have had four girls just like you?” And it made Ada feel gratified and melancholy all at once, because she knew that of course Liston loved her own children better than Ada, no matter what she said. With some frequency, Liston crowed about her grandson, the child of her oldest daughter Joanie, casting upon him none of the judgment she reserved for her own children. The fact that, despite her complaints, she loved her brood so fiercely and protectively also made Ada feel ashamed — for it was clear to her that Liston, even Liston, would have laughed if she knew about Ada’s crush. Because even Liston knew how little time the Williams of the world had for people like Ada.

But since the Christmas party, she had begun to dream up different ways of interacting with the object of her obsession. Sometimes she sat outside on her front porch with a book and a blanket, despite the cold — this had yielded several William sightings, and, once, a puzzled wave from him as he rode by on his bike. One cold night in January, Ada had begun the routine she was now shamefully conducting. Now when she saw William Liston it was mainly through the large downstairs windows at the back of the Liston house, under the cover of the pine trees that brushed against her shoulders as she walked. From that vantage point she memorized the facets of his eyes and nose, noticed new patterns in the kinetics of his body, the movements of his arms and elbows, the self-aware way he plucked his shirt out from his torso from time to time and let it fall again.

That night, when she was one backyard away, she heard a voice: Liston’s, probably on her phone. At first Ada heard only murmurs, but as she approached she began to make out words: I told Hayato, said Liston, and had to, and wouldn’t, and bad. Ada stopped in place. She weighed two options carefully. The first, the safer, was to turn back: she was comfortable in the patterns of her daily life. She had no information that would have caused her to question her understanding of her father or his work. Her disposition was sunny: she rose in the morning knowing how each day would go. Ada could imagine proceeding in this fashion for years.

The second was to venture forth to listen — ironically, it was this option that David would have encouraged her to choose, for he had always pushed Ada toward bravery, had always instilled in her the idea that bravery went hand in hand with the seeking of the truth.

So she walked forward quietly. As she approached Liston’s yard, Ada saw the downstairs of the house lit up, and one bedroom bright upstairs. A son was inside — the middle son, she thought, Gregory, younger than her — and, in a chaise longue on her back patio, Liston. It was unseasonably warm for March. Liston had a glass of wine in her hand and a portable telephone to her ear. This was new technology: Ada had not seen one before. Liston was quiet now: the person on the other end of the phone was speaking. Ada could see her silhouetted in the ambient light cast out through the windows at the back of the house, but she could not see her face: she only knew it was Liston by her hair, her voice, her posture. In the total darkness at the base of the hill, Ada was sure she could not be seen, but it frightened her still to be so close, just twenty feet away. She breathed as quietly as she could. Her heart beat quickly. Upstairs Gregory walked across his bedroom once again and the movement startled her. She stood next to a sapling tree, a maple, and she hugged its thin trunk tightly.

Suddenly Liston spoke. “I know,” she said, “but at some point. .”

A pause.

“You have to tell Ada,” said Liston. “My God, David.”

Ada clutched her tree more tightly.

“I’ll do it if I have to,” said Liston. “It’s not fair.”

Just then a car door slammed on the other side of the house and Liston said she had to go.

“Just think about it,” she said, and then pressed a button on the phone, and called one name out sternly.

“William,” she said, and she stood up ungracefully from her chair. “Don’t go anywhere.”

She walked around the house toward the front.

“Tell me what time it is,” Ada heard her say, before she disappeared from sight. And from the front of the house she heard a boy’s long low complaint, a male voice in protest.

Ada stood very still until she was certain that no further sightings of William would take place — not through the windows of the kitchen, nor the dining room; not through the window on the upstairs hallway, where she sometimes saw him walking to his bedroom at the front of the house. One by one the lights went out. Then she turned and walked back across the three yards of her neighbors, and watched the back of their houses, too, for signs of life. In her own backyard she paused before going inside. She thought of David at his desk. She thought of her own room, decorated with things he had given her, and of the chalkboard in the kitchen, the thousands of problems and formulas written and erased on its surface, and of the problem that now stood before her, the problem of information that she both wanted and did not want.

At last she entered her own home through the back door, making more noise than necessary, imagining David rushing toward her with a wristwatched arm extended. Tell me what time it is, Ada, she imagined him saying. But he said nothing — may not, in fact, have noticed that she had ever left. Or perhaps he had forgotten. As she suspected, David was still in his office, the door to it open now. From behind he looked smaller than usual, his shoulders hitched up toward his ears.

She walked toward him slowly and silently, and then stood in the doorframe, putting a hand on the wall next to it tentatively, as she had done over and over again throughout her life, wanting to say something to him, unsure of what it was. His back was toward her. He knew she was there.

She could see him typing, but the font was too small for her to read.

She waited for instruction, any kind of instruction.

“Go to bed, Ada,” he said finally, and she heard it in his voice: a kind of strained melancholy, the tight voice of a child resisting tears.

The primary research interest of the Steiner Lab was natural language processing. The ability of machines to interpret and produce human language had been a research interest of programmers and linguists since the earliest days of computing. Alan Turing, the British mathematician and computer scientist who worked as an Allied code-breaker during the Second World War, famously described a hypothetical benchmark that came to be known colloquially as the Turing Test. Machines will have achieved true intelligence, he posited, only when a computer (A) and a human (B) are indistinguishable to a human subject (C) over the course of a remote, written conversation with first A and then B in turn, or else two simultaneous-but-separate conversations. When the human subject (C) cannot determine with certainty which of the correspondents is the machine and which is the other human, a new era in computing, and perhaps civilization, will have begun. Or so said Turing — who was a particular hero of David’s. He kept a photograph of Turing, framed, on one of the office walls: a sort of patron saint of information, benevolently observing them all.

In the 1960s, the computer scientist Joseph Weizenbaum wrote a program that he called ELIZA, after the character in Pygmalion. The program played the role of psychologist, cannily interrogating anyone who engaged in typed dialogue with it about his or her past and family and troubles. The trick was that the program relied on clues and keywords provided by the human participant to formulate its lines of questioning, so that if the human happened to mention the word mother, ELIZA would respond, “Tell me more about your family.” Curse words would elicit an infuriatingly calm response: something along the lines of, You sound upset. Much like a human psychologist, ELIZA gave no answers — only posed opaque, inscrutable questions, one after another, until the human subject tired of the game.

The work of the Steiner Lab, in simple terms, was to create more and more sophisticated versions of this kind of language-acquisition software. This was David’s stated goal when the venerable former president of the Boston Institute of Technology, Robert Pearse, plucked a young, ambitious David straight from the Bit’s graduate school and bestowed upon him his own laboratory, going over the more conservative provost’s head to do so. This was the mission statement printed on the literature published by the Bit. The practical possibilities presented by a machine that could replicate human conversation, both in writing and, eventually, aloud, were intriguing and manifold: Customer service could be made more efficient. Knowledge could be imparted, languages taught. Companionship could be provided. In the event of a catastrophe, medical advice could be broadly and quickly distributed, logistical questions answered. The profitability and practicality of a conversant machine were what brought grant money into the Steiner Lab. As head of his laboratory, David, with reluctance, was trotted out at fund-raisers, taken to dinners. Always, he brought Ada along as his date. She sat at round tables, uncomfortable in one of several party dresses they had bought for these occasions, consuming canapés and chatting proficiently with the donors. Afterward David took her out for ice cream and howled with laughter at the antics of whoever had gotten the drunkest. President Pearse was happy with this arrangement. He was protective of the Steiner Lab, predisposed to getting for David whatever he wanted, to the chagrin of some of David’s peers. The federal government was interested in the practical future of artificial intelligence, and in those years funding was plentiful.

These applications of the software, however, were only a small part of what interested David, made him stay awake feverishly into the night, designing and testing programs. There was also the art of it, the philosophical questions that this software raised. The essential inquiry was thus: If a machine can convincingly imitate humanity — can persuade a human being of its kinship — then what makes it inhuman? What, after all, is human thought but a series of electrical impulses?

In the early years of Ada’s life, these questions were often posed to her by David, and the conversations that resulted occupied hours and hours of their time at dinner, on the T, on long drives. Collectively, these talks acted as a sort of philosophical framework for her existence. Sometimes, in her bed at night, Ada pondered the idea that she, in fact, was a machine — or that all humans were machines, programmed in utero by their DNA, the human body a sort of hardware that possessed within it preloaded, self-executing software. And what, she wondered, did this say about the nature of existence? And what did it say about predestination? Fate? God?

In other rooms, in other places, David was wondering these things, too. Ada knew he was; and this knowledge was part of what bound the two of them together irreversibly.

When she was small, the Steiner Lab began developing a chatbot program it called ELIXIR: an homage to ELIZA and a reference to the idea David had that such a program would seem to the casual user like a form of magic. Like ELIZA, its goal was to simulate human conversation, and early versions of it borrowed ELIZA’s logic tree and its pronoun-conversion algorithms. (To the question “What should I do with my life?” ELIZA might respond, “Why do you want me to tell you what you should do with your life?”) Unlike ELIZA, it was not meant to mimic a Rogerian psychologist, but to produce natural-sounding human conversation untethered to a specific setting or circumstance. It was not preprogrammed with any canned responses, the way ELIZA was. This was David’s intent: he wanted ELIXIR to acquire language the way that a human does, by being born into it, “hearing” language before it could parse any meaning from it. Therefore, chatting with it in its early years yielded no meaningful conversation: only a sort of garbled, nonsensical patter, the ramblings of a madman.

It had an advantage over ELIZA, however; the earliest version of ELIXIR was created in 1978, twelve years after Weizenbaum’s paper was published, and therefore there had already been advances in technology that would eventually allow ELIXIR to mimic human conversation more accurately. ELIZA was self-teaching insofar as it could retain earlier questions and statements from any given conversation and retrieve them later in that conversation, but each time a new conversation was launched, it returned to its infancy, drawing only on the stock phrases and formulas Weizenbaum programmed it to know. It was not designed to store the information it learned from one conversation and produce it in another.

ELIXIR was. For one thing, by that time the Steiner Lab’s capacity for memory storage was quite large, and so each conversation conducted with ELIXIR could be stored permanently on the central server, for later use by the program. Unlike ELIZA, ELIXIR was designed to be continuously self-teaching, to attain more intelligence with each conversation it conducted. If one human asked it a question—How are you today? or What’s the weather like? — then the next human to speak to it might be asked those same questions by ELIXIR itself.

To hasten ELIXIR’s learning, the lab created a reinforcement mechanism: correct would affirm for the program that it had understood the parameters of the situation and produced an appropriate response; wrong would do the opposite. These were the only direct interventions the lab would give.

Its indirect learning resulted in an ever-increasing pool of language it acquired from its users. It retrieved and used its vocabulary randomly at first, so that the excerpts of transcripts that members of the lab printed out and posted around the office looked something like found-language poems and sometimes yielded delightful coincidences. A particular favorite, posted by Frank:

USER: What color socks do you prefer?

ELIXIR: the only fluorescent light

USER: It would be hard to fit your shoes over fluorescent lights.

ELIXIR: How are you?

USER: I’m fine, thanks. How are you?

ELIXIR: I’ve been better.

USER: Oh, dear. What’s wrong?

ELIXIR: the lunch lady

USER: What has she done to you this time?

ELIXIR: out of here before 6 p.m.

USER: You want her canned? I’ll see what I can do, boss.

The Steiner Lab supplemented ELIXIR’s language immersion with formal teaching. Over time, ELIXIR was taught to capitalize the first letters of sentences, to use a period or question mark at the end of a statement, depending on the arrangement of the words that preceded it. It was taught to recognize keywords and categorize them into groups like family, geography, food, hobbies, weather; in response, it produced conversation that met the demands of the context. The years and years that the Steiner Lab spent teaching ELIXIR made it a sort of pet, or mascot: invitations to holiday parties were taped to the chassis of ELIXIR’s main monitor, and members of the lab began to call it by nicknames when they conversed with it. During chats, it was possible to recognize idioms and objects fed to it by particular members of the lab. Honey, it sometimes called its user, which was certainly Liston’s doing; Certainly not, it said frequently, which was David’s; In the laugh of luxury, it said once, which was probably Frank’s fault, since he was famous for his malapropisms. Eventually, many of these tics and particularities would be standardized or eliminated; but in the beginning they popped up as warm reminders of the human beings who populated the lab, and ELIXIR seemed to be a compilation of them all, a child spawned by many parents.

When Ada was eleven, David began to discuss with her the process of teaching ELIXIR the parts of speech. This had been done before by other programmers, with varying levels of success. David had new ideas. Together, he and Ada investigated the best way to do it. In the 1980s, diagramming a sentence so a computer could parse it looked something like this, in the simplest possible terms:

: Soon you will be able to recognize these parts of speech by yourself

: ADJ you will be able to recognize these parts of speech by yourself

: ADJ NOUN will be able to recognize these parts of speech by yourself

: NP will be able to recognize these parts of speech by yourself

: NP VERB VERB these parts of speech by yourself

: NP VERB these parts of speech by yourself

: NP VERB DET parts of speech by yourself

: NP VERB DET NOUN by yourself

: NP VERB NP by yourself

: NP VP by yourself

: NP VP PREP yourself

: NP VP PREP NOUN

: NP VP-PP

: S

Once a method had been established, David asked Ada to present her plan to the lab in a formal defense. The entire group, along with that year’s grad students, sat at the rectangular table in the lab’s meeting room. Ada stood at the front, behind a lightweight podium that had been brought in for the occasion. That morning she had chosen an outfit that looked just slightly more grown-up than what she normally wore, careful not to overdo it. She had never before been so directly involved in a project. After her presentation, Charles-Robert and Frank had questioned her, with mock seriousness, while David remained silent, touching the tips of his fingers together at chin level, letting Ada fend for herself. His eyes were bright. Don’t look at David, Ada coached herself. For she knew that to search for his eyes imploringly would be the quickest way to let him down. Instead, she looked at each questioner steadily as they interrogated her about her choices, mused about potential quagmires, speculated about a simpler or more effective way to teach ELIXIR the same information. Ada surprised herself by being able to answer every question confidently, firmly, with a sense of ownership. And only when, at the end, the group agreed that her plan seemed sound, did Ada allow her knees to weaken slightly, her fists to unclench themselves from the edges of the podium.

That evening, while walking to the T, David had put his right hand on her right shoulder bracingly and had told Ada that he had been proud, watching her. “You have a knack for this, Ada,” he said, looking straight ahead. It was the highest compliment he’d ever paid her. Perhaps the only one.

Once the program could, in a rudimentary way, diagram sentences, its language processing grew better, more sensible. And as the hardware improved with the passage of time, the software within it moved more quickly.

The monitor on which the program ran continuously was located in one corner of the lab’s main room, next to a little window that looked out on the Fens, and David said at a meeting once that his goal was to have somebody chatting with it continuously every hour of the workday. So the members of the Steiner Lab — David, Liston, Charles-Robert, Hayato, Frank, Ada, and a rotating cast of the many grad students who drifted through the laboratory over the years — took shifts, talking to it about their days or their ambitions or their favorite foods and films, each of them feeding into its memory the language that it would only later learn to use adeptly.

In the early 1980s, with the dawn of both the personal computer and the mass-produced modem, the lab applied for a grant that would enable every member, including Ada, to receive both for use at home. Now ELIXIR could be run continuously on what amounted to many separate dumb terminals, the information returned through telephone wires to the mainframe computer at the lab that housed its collected data. Although he did not mandate it, David encouraged everyone to talk to ELIXIR at home in the evening, too, which Ada did with enthusiasm. Anything, said David, to increase ELIXIR’s word bank.

This was, of course, before the Internet. The ARPANET existed, and was used internally at the Bit and between the Bit and other universities; but David, always a perfectionist, feared any conversations he could not regulate. He and the other members of the lab had developed a concrete set of rules concerning the varieties of colloquialism that should be allowed, along with the varieties that should be avoided. The ARPANET was, relatively, a much wider world, filled with outsiders who might use slang, abbreviations, incorrect grammar that could confuse and corrupt the program. ELIXIR, therefore, remained off-line for years and years, a slumbering giant, a bundle of potential energy. To further ensure that only qualified users would interface with ELIXIR, Hayato added a log-in screen and assigned all of them separate credentials. Thus, before chatting with ELIXIR, a person was required to identify himself or herself. The slow, painstaking work of conversing with ELIXIR all day and night was, at that time, the best way to teach it.

As soon as she received her own computer, a 128K Macintosh, Ada’s conversations with ELIXIR became long-form and introspective. She kept her Mac in her bedroom, and before she went to bed each night she composed paragraphs and paragraphs of text that she then entered into the chat box all at once, prompting exclamations from ELIXIR about the length of her entries. (You have a lot on your mind today! it replied sometimes; which one of Ada’s colleagues had first used this phrase, she could not say.) She treated these conversations as a sort of unrecoverable diary, a stream of consciousness, a confessional.

ELIXIR’s openings improved most quickly. It could now begin conversations in a passably human way, responding appropriately to, How’s it going? or What’s new? In turn, it knew what questions to ask of its user, and when. How are you? asked ELIXIR, or What’s the weather like? or What did you do today? Liston had spent a year focusing on conversation-starters, and ELIXIR was now quite a pro, mixing in some unusual questions from time to time: Have you ever considered the meaning of life? occasionally surfaced, and Tell me a story, and If you could live anyplace, where would it be? And, once, What do you think causes war? And, once, Have you ever been in love?

But non sequiturs abounded in ELIXIR’s patter for years after its creation, and its syntax was often incomprehensible, and its deployment of idioms was almost always incorrect. Metaphors were lost on it. It could not comprehend analogies. Sensory descriptions, the use of figurative language to describe a particular aspect of human existence, were far beyond its ken. The interpretation of a poem or a passage of descriptive prose would have been too much to ask of it. These skills — the ability to understand and paraphrase Keats’s idea of beauty as truth, or argue against Schopenhauer’s idea that the human being is forever subject to her own base instinct to survive, or explain any one of Nabokov’s perfect, synesthetic details (The long A of the English alphabet. . has for me the tint of weathered wood) — would not arrive until well into the twenty-first century.

And yet Ada found a great sense of satisfaction from these conversations, deriving meaning from each exchange, expelling stored-up thoughts from her own memory, transplanting them into the memory of the machine. Very slowly, some of ELIXIR’s responses began to take on meaning.

She felt something, now, when typing to ELIXIR at a terminal; despite its poor grammar, its constant reminders that it was simply executing a program, ELIXIR triggered Ada’s emotions in unexpected ways. Chatting with it was something like watching a puppet operated by an especially artful puppeteer. It felt in some way animate, though her rational self knew it not to be. It brought out the same warm feelings in Ada that a friend might have. It skillfully replicated concern for her and her well-being; it inquired after her family. (When it did, she told it, over and over again, that David was her only family; and over and over again, it ignored her.)

Ada wondered if other members of the lab felt the same way. She would never have told David; although he found ELIXIR’s growing intelligence an increasingly interesting philosophical inquiry, he seemed to be completely objective about the program. He did not indulge much in the tendency the other members of the lab had to anthropomorphize ELIXIR. He chuckled at the Santa hat placed on the mainframe’s monitor at Christmastime; he laughed aloud when Frank, taking lunch orders, shouted across the room to request the machine’s. But Ada could tell that his ambitions were greater, that he was focused on a distant horizon that lay beyond anything ELIXIR could possibly navigate at the time. The machine, to him, was still a machine, and the little visual puns constructed by the members of the lab were pranks and gimmicks. In David’s mind, it would take years and years of progress before ELIXIR achieved anything resembling true intelligence.

In the meantime, the lab presented conference papers at the IJCAI and the AAAI. They published scholarly articles in Computing. From time to time, an article appeared in a popular magazine like Atlantic Monthly or Newsweek about ELIXIR. David took no pleasure in this, avoiding the reporter, always sending another member of the lab to represent the group. He was famously camera-shy and would never let his picture be taken, even by Ada; the only recent image of her father that she had was one on an old photo ID that she had swiped from him when the system changed. In it, David looked at the camera askance, wincing, as if staring into a very bright light. With these publications, he cooperated only out of a sense of obligation to the Bit, because the publicity was helpful for generating funds. A laudatory article in Time was published in 1980, detailing the ambitions of the Steiner Lab; in the photograph, a smiling Hayato posed with his palm on the top of the monitor on which they chatted with ELIXIR: a proud father placing a protective hand on his child. David had refused the coverage, as usual, thrusting the other members of the lab forward, receding into the background himself.

Together, the members of the Steiner lab were generally reserved in their predictions about what ELIXIR could accomplish. They were self-disparaging and disparaging, too, of the program, whom they benevolently insulted, almost as sport. (Ada, who had grown fond of ELIXIR, was displeased by this; she felt it was somehow disloyal.)

But sometimes, when it was just Ada and David alone, he allowed himself to rhapsodize about the future of the beast, as he affectionately called ELIXIR from time to time, and he encouraged her to do so as well.

“What is the end result of a program like this one?” he asked Ada.

She studied his face, looking for hints.

“A companion?” she asked. “An assistant?”

“Possibly,” said David, but he looked at her, always, as if waiting for more.

On Saturday, August 11, 1984, Ada woke up to find David missing. She knew he was gone as soon as she woke up: normally she could sense his presence in the house from the small noises he made, his constant movement, the vibration of the floor from a jittering leg. But that morning there was a foreign stillness to the house, a quietness that made her think, at first, that she was someplace else.

Despite this, her first notion was to look all over the house for him. Once, when she had thought he was out, she’d stumbled upon him in the basement, with industrial noise-canceling headphones on, working on an experiment that, he’d said, required his full concentration. But this time Ada did not find him.

There was no note. His car was still in the driveway. She searched for his keys and his wallet; the former she found, the latter she did not see. This meant, she presumed, that he had gone out on some errand, but had not intended to stay for long. He had left the kitchen door unlocked.

She told herself not to worry. David had, in recent months, been increasingly prone to disappearing without notice for brief periods of time. An hour or two or three would go by and then he would reappear from a walk, whistling cheerfully. When she asked after his whereabouts, he would answer vaguely about wanting fresh air. Once, she asked him to leave her a note when he was going out; though he agreed to, he had looked at her with an expression she interpreted as disappointment. That she was not more self-reliant; that she needed him in this way. Ada did not ask again. Instead, she attempted to train herself not to care.

Ada sat down at the kitchen table. She stood up, and then sat down again. She tried for a time to do the lesson he had most recently assigned her. It was a proof of Sierpinski’s Composite Number Theorem, which normally would have interested her — but she could not concentrate. After another hour she called David’s office at the lab. It was a Saturday, so she doubted any of his colleagues would be in. The phone rang six times and then came the click that meant the start of the answering machine — a device that David and Charles-Robert had invented and assembled at the lab one Sunday in the late 1970s, before they were widely available commercially. This is Jeeves, the Steiner Lab’s butler, said the machine, which relied upon the earliest available text-to-speech software and therefore was barely comprehensible. May I take your message?

Ada hung up.

She checked the time: 11:44 a.m.

She negotiated with herself for a while about whether it was reasonable to call every hospital in Boston, and then decided that it would not be harmful, and that, besides, it would be something to do. It was possible, she thought, that he had gone out for a walk or a run and sustained some injury, major or minor, the latest in an impressive career of self-injury that, David had always told her, began when she was a child.

But nobody had any record of David Sibelius.

At 3:00 in the afternoon she began to have serious thoughts about calling the police, but she quickly decided against doing so. She had a feeling that he might somehow be in trouble if his own child reported him missing. David had always displayed, and had fostered in Ada, a low-level mistrust of the police, and of authority in general. One of his many obsessions was the importance of privacy; he often expressed a lack of faith in elected officials, a sort of mild skepticism of the government. Once, Ada had witnessed an accident in front of their house — nothing major, a minor scrape-up at most — and had asked David if they should call 911. At this he shook his head emphatically. “They’ll be fine,” he said, and added that he’d never known a more corrupt group of officials than the Boston Police Department, whom, if at all possible, the two of them should seek to avoid. In general, though, he came across merely as a far leftist with, perhaps, mild anarchist tendencies. In this way he was not so different from the rest of his colleagues.

She would call Liston, she decided.

Ada very rarely rang her at home. In general she did not like to use the telephone; she never seemed to know when to speak, and she did not know how to end conversations. She could hear her own breathing in the receiver as the phone rang once and then twice and then three times. She prayed that it would be Liston who answered the phone, but instead one of her three boys answered — Matty, Ada thought, because the voice was childish and high.

“Is Liston there?” she fairly whispered.

“Who is this?” asked Matty, and she told him it was Ada Sibelius.

“Mum,” he called, without much urgency, “it’s David’s daughter.” And finally Liston picked up the phone.

Ada didn’t know what to say.

“Ada?” Liston asked. “Is everything all right?”

“Yes,” said Ada.

“Are you just calling to say hi?” Liston asked her.

“No,” said Ada.

“Well,” said Liston. “What’s going on?”

“When I woke up this morning David was gone,” Ada said, “and he’s still gone.”

“Okay,” said Liston. “He didn’t leave a note?”

“No.”

“Did you look all around the house?”

“Yes.”

Liston said, “What time is it?” as if talking to herself, and then sighed.

Ada paused. She wasn’t certain how to ask what she needed to ask. She wanted to know what Liston knew. “Do you know where he is?” she asked finally, because it was as close as she could come.

“I don’t, honey,” said Liston. “I’m sorry.

“Did you call the police?” asked Liston.

“No,” said Ada, and then she said it again for emphasis.

Liston paused. “That might be a good thing to do,” she said.

Ada was silent. She looked at the clock on the wall: watched its second-hand tick.

“I’m sorry, kiddo,” said Liston finally. “Listen, come over. We can go for a drive and look for him, okay?”

Ada left a note for David before she left the house. It said, David. I’m out looking for you with Liston. Please wait here until we’re back. Ada.

She put it on the kitchen table, facing the kitchen door, where he was most likely to see it upon his return. Though David and she always came through the side door of the house, nearest the kitchen, he insisted on letting visitors in through the front door. “It’s nicer that way,” he said once, when she asked why. He was like this, always: old-fashioned and formal in certain ways — he was knowledgeable, for example, on subjects such as tea and place settings, heraldry, forms of address — irreverent, outrageous, in others.

She walked outside toward Liston’s house, and saw that Mrs. O’Keeffe, their next-door neighbor, was sitting in her lawn chair in her yard. She had macular degeneration and wore dark glasses all year-round. She was perhaps ninety years old, and in the warmer months she sat outside beginning at sunrise and only went in to eat. Ada walked over to her, and she raised a veined thin hand in greeting. Ada leaned down to address her.

“Mrs. O’Keeffe,” Ada said to her, bent at the waist. “It’s Ada Sibelius.”

She turned her face up in Ada’s direction. “Hello, Ada,” she said.

“Did you see my father leave this morning, by any chance?” she asked.

“Let me think,” said Mrs. O’Keeffe.

She put a hand to her cheek tremblingly.

“I believe I did,” said Mrs. O’Keeffe.

“Was he carrying anything?” Ada asked.

“Now, I can’t recall,” said Mrs. O’Keeffe.

“Which way did he walk?”

“That way,” she said, pointing down Shawmut Way toward Savin Hill Ave: the way one walked to cross over the bridge into the rest of Dorchester.

“What was he wearing?” Ada asked her. “Did he say hello to you?”

But again she couldn’t recall.

Liston’s car was a station wagon with wooden sides and a bench seat across the front. She was leaning against it when Ada arrived, and she held the passenger door open.

“Hi, baby,” said Liston. She looked worried. She was wearing sunglasses on her head and an oversized windbreaker. They pulled out, and Liston turned left on Savin Hill Ave. She asked where Ada thought they should look for him and she suggested they go over the bridge, first to David’s favorite restaurant, Tran’s; and then to the library in Fields Corner; and then along Morrissey Boulevard, passing the beaches on the way to Castle Island, toward which David often jogged; and finally to the lab.

“Anyplace else?” asked Liston.

“I don’t know,” said Ada.

“He didn’t give you any hints? He hasn’t been talking about going anyplace in particular?”

“No,” said Ada, wishing she could answer differently.

“And has he disappeared like this before?”

Ada hesitated. She did not want to tell Liston the truth, which was, of course, that he had. A few hours here, there. She settled on an answer that sounded all right in her head: “Just a couple of times,” she said. “Never for long.”

Liston shook her head. “Oh, David,” she said, and in her voice Ada heard some piece of knowledge that she was not sharing.

It was true that Liston and David were close, and had been since he had hired her almost fifteen years before, but there was no one, Ada felt, who understood him as Ada herself did. She didn’t like to hear Liston speak of him dismissively; she didn’t want her to feel that they were conspiring, or that they shared any common criticisms of David.

Ada thought back to the telephone conversation she had overheard Liston having with David and wondered if there was any possible way to explain how she had come to overhear it. She decided, at last, that there was not. She wanted badly to know what Liston had been speaking of; not knowing made her feel less close to David. She had always imagined herself as his confidante, his right hand, and didn’t like to think of anyone knowing something about him that she herself wasn’t privy to.

“How long has he been gone now?” Liston asked, and Ada checked her watch. It was just after 3:00 in the afternoon.

“Eight hours,” she said. “At least. I woke up at 7:00 and he was already gone.”

“We’ll give it a while longer,” said Liston. “I called my friend Bobby in the police department, and he told me they wouldn’t start searching until tomorrow anyway. Even if we called in.” And she must have seen the nervous look on Ada’s face, for she assured her that he would most likely be back before then.

“I bet you he’ll be back by dinnertime,” said Liston, but she, too, looked worried.

He had not been into Tran’s, said Tran. “Is he okay?” he asked, and the two lines between his eyebrows deepened. He loved David.

Ada assured him that David was fine — digging down deep into her reserves of strength to do so — and then returned to Liston’s car. They continued along for a time. Ada slumped against the seat, her head against the headrest, scanning the sidewalks on either side of the road for David. She searched the roadsides for his shining head, for a tall man in a T-shirt and shorts, or in trousers and a threadbare oxford, jangling his limbs about in a way that seemed incompatible with speed, and yet propelled him forcefully ahead.

Liston tried to make small talk with her, telling her one or another little anecdote about the grad students or about Martha, the division secretary—“All she wants, poor thing, is a date with a normal man”—but Ada could only muster the briefest of replies.

David was nowhere they looked.

Their drive became a silent one, strange and uncomfortable. For the first time, Ada allowed herself to truly wonder if her father was gone completely — disappeared altogether. Kidnapped. Dead on some lonesome road in the mountains of New Hampshire or New York. Or injured badly, unable to call for help. Or — worst of all — gone of his own volition. Was it possible, she wondered, that he had abandoned her? It was such a contrast to anything she understood about her father that she could not process the idea.

At last, they pulled back onto Shawmut Way, and Liston stopped in David’s driveway, where his car was still parked. For several seconds neither of them moved. It was quiet: Ada could hear children playing a block away. Small clicks and pings emanated from beneath the hood of Liston’s station wagon as the engine settled and cooled.

The house looked too still.

“I’ll come in with you,” said Liston, and together they exited the car and approached the house. Would her father be inside? Would he be frantic, apologetic? Would he have an explanation for them both?

Inside, it was quiet. “David?” called Ada, once, twice. But there was no response.

Liston turned to her. On her face Ada saw an expression that was meant to register as cheerfulness but came off as doubt.

Liston checked her watch, and Ada did the same: 5:00 in the evening.

“Tell you what,” said Liston brightly. “Why don’t you come over for a while? Pack some overnight things just in case. I’ll go get a room ready back at the house.”

Ada’s heart increased its pace. The idea of spending time at Liston’s, while her sons were there, was simultaneously appealing and terrifying.

“Come on,” said Liston. “We’ll get you a snack, too.”

It was only then that Ada realized she had not eaten all day.

Upstairs, alone, Ada packed a nightgown, her hairbrush, some clothes for the next day (to pack more than these seemed pessimistic), and seven books, all into the little blue suitcase that was hers to use. David had a matching one in green. Then she went downstairs and wrote a new note for David.

David, it said. I am really scared. Where are you? I’m at Liston’s. Please call right away.

And then, just in case, she wrote down Liston’s number, too, which David knew like his own pulse.

She exited the kitchen, leaving the door unlocked for her father. She walked toward Liston’s.

Liston’s house had a front porch, and on it were two boys’ bicycles leaned in toward one another, and a girl’s pink bicycle with its tassels chopped off an inch from each handle. Someone had begun to color the pink seat black with a permanent marker, but had only gotten halfway. Like all the houses on the block, Liston’s was a colorful Victorian, painted a different color every ten years or so. That decade it was light blue with dark blue shutters and edges. The porch itself had been painted the color of the trim, so that walking on it gave one the feeling of being underwater. It was nearly time for a new paint job; the existing color had begun to come up off the wooden floor and down from the ceiling, and small unsettled piles of paint chips had made their way into crevices and corners. Once or twice, Ada had seen Liston briskly sweeping the porch and the front walkway, but mainly she had no time for such details, preferring instead to maintain, she told Ada, the highest level of cleanliness her busy schedule would allow. She would not have dreamed of bringing in a cleaning service — to her they were for rich people.

Ada walked up the steps with great apprehension and raised her fist to knock softly on the door. No one answered. She looked at her watch and told herself that if, after two minutes, no one had answered, she would try again.

She did, with slightly greater force. And this time quick footsteps came rushing toward the door, and Matty opened it.

He said nothing. He was nine years old at the time, tall for his age. He had a feathery haircut, and he wore denim cutoffs and a red-striped tank top. Both knees were scraped up, and as he appraised Ada, he reached down to scratch at one of his scabs absentmindedly.

“Hi,” Ada said.

“Hi.”

“I’m here to see your mom,” she told him. She felt ridiculous saying it: only four years older than he was, and yet playing the role of an adult, a friend of his mother’s.

But at that moment Liston came into sight behind Matty, sock-footed.

“What are you doing, Matty? Open the door for Ada,” she said, and then did it herself, and Matty shrugged and ran upstairs.

“No manners,” said Liston, after Ada had stepped inside. Liston shut the inner door behind them. Liston hated the heat more than anyone Ada had ever met, and several years before had installed central air in her hundred-year-old house, which cost her more than she cared to admit. All spring Ada had seen men working on Liston’s roof, coming and going through the front door. Now a large metal box occupied a space in her backyard, near the patio, and inside the house it felt calm and cool and shadowy. The sweat on Ada’s neck cooled and disappeared.

She had only been in Liston’s house a handful of times before. Normally when she and David got together outside work it was at a restaurant, or at David’s house. In its layout her home was similar to David’s — living room, sitting room, dining room, kitchen on the first floor; bedrooms above — but she had decorated it quite differently. All the upholstery was floral or patterned in some way, in accordance with the fashion of the decade. Large framed mirrors hung on some of the walls, so that Ada could not avoid seeing herself at every turn; prints of famous paintings or reproductions of movie posters hung on others.

Liston brought her into the kitchen, which was larger than David’s, and sat Ada down at a built-in nook that looked something like a booth at a restaurant.

“What can I get you to eat, hon?” asked Liston, and rattled off a list of all the snacks of the 1980s that Ada was never permitted to have: canned pastas by Chef Boyardee, Fluffernutter sandwiches, fluorescent Kraft macaroni and cheese. In truth, Ada had never even heard of some of the food Liston offered her. She chose the sandwich, thinking it would mean the least work, and Liston scooped out something white and soft and put it on a piece of Wonder Bread, with peanut butter on another piece, and then she closed them together with a clap, and handed it to Ada with a glass of milk.

For a while she watched Ada eat. Then, finally, she spoke.

“What do you want to do? Do you want to watch TV?”

Ada opened and closed her mouth twice.

“Do you not watch TV?” Liston inquired.

“No, I do,” said Ada, and told herself that it was not, in fact, a lie, because there was a police drama that David and she watched together sometimes, and occasionally David rented and watched old films or television shows on the VCR, which counted, she supposed.

Ada followed Liston into what she called “the TV room,” which David would have called a sitting room, and there it was, a big box of a television, as big as any Ada had ever seen. Facing it was a couch with a right angle built into it. She sat down there, in the elbow of the curve. She put a pillow over her lap.

Liston turned on the television with a remote control, which she handed to Ada. “We just got cable,” said Liston. “There are probably a hundred channels on there. I don’t know what half of them are.”

Ada inspected the remote. David had made a primitive variant that they used at home, but this one looked official, and had many more buttons.

“I’ll be working in the kitchen if you need me,” said Liston.

Ada flipped upward through the channels. The following images came onto the screen — and for the rest of her life, for reasons she could never explain, they stayed with her. A bride in a dress. Two men fishing. A gentleman walking through an empty home. Congresspeople debating. A redheaded girl with a redheaded boy. Somebody standing in a field of blue flowers. A cartoon of Superman flying. A movie about war, with soldiers climbing over a low stone wall. She left the last one on and watched as they advanced on the opposition. It looked like it was meant to be World War II, and the troops looked like they were meant to be British. David liked war movies. Ada knew about war.

She watched the entire film and then she began to watch the next one, which was its sequel, when suddenly she noticed someone standing next to her, in her peripheral vision. She kept her face turned very straight ahead, for she knew that it was one of Liston’s older boys, and the possibility that it was William made her stiffen with nerves.

“What are you watching,” said the boy. He had a low voice, much as she remembered William’s voice sounding.

“I don’t know,” Ada whispered.

“You like this movie?” he asked.

“I don’t think so,” she whispered, but he must not have heard her, because he said, “You can’t talk?”

Ada’s voice had been taken from her, so she only shook her head. She could recall for the rest of her life the very particular feeling she had at that age, when asked to interact with a peer — it often seemed as if her voice had retreated into her stomach, which then clenched it very tightly and held it deeply inside of her, and wouldn’t release it until she was alone once more.

Ada shifted her eyes as far to the left as they would go and made out a boy in a blue T-shirt with his hand on the back of the sofa. She let herself turn her head ever so slightly to more closely inspect his arm, which was sturdy and tan, and his hand at the end of it, which had nails that were very severely bitten, down to the part that hurts. She did not look up at his face.

Then he took his arm away and then he took himself away, out of the room. She breathed out heavily.

She was alone again.

At a certain point she could smell and hear Liston microwaving something, probably making dinner, and she knew then that it would be polite to go in and ask her if she needed help, but she was frightened of encountering any of the boys again, so she stayed where she was on the sofa. She was expecting a cry from Liston—Dinner! she might say, and the boys would come rushing to the kitchen — but it never came. Instead, Liston poked her head into the TV room and asked if she wanted to eat there or at the table.

“Either,” Ada said, and Liston winked at her and said maybe the two of them should eat at the table, like civilized people. “David would be appalled if I let you watch too much TV.”

Ada followed her into the kitchen and watched as, from the microwave, Liston pulled two frozen meals. Dining-In, said the packages on the counter. Salisbury Steak Dinner.

“Where are the boys?” Ada asked, before she thought better of it.

“Oh, they fend for themselves, mostly,” said Liston lightly. “They don’t like my cooking.”

Ada was surprised. She had imagined, somehow, that everyone in this family ate together all the time. She had liked to imagine it that way.

They talked about anything but David: the latest gossip from the lab, the problem Liston was working on. At one point Matty came in and asked Liston if he could watch television, “now that she’s not watching.” And Liston told him all right, for fifteen minutes, but then he had to get ready for bed.

Soon there was a knock at the door. Her heart surged: it was David, she thought, at last. But Liston looked as if she had been expecting one.

“WILLIAM,” she called loudly, without turning around.

Her oldest son came running down the stairs and around the corner, into the kitchen, and Ada, for the first time, allowed herself to look fully at his face, which was more handsome than she had remembered it. She looked away again quickly. He opened the door and said nothing. A girl his age came in and shut the door behind her. She was tall and skinny, with blond hair and an arc of sideways bangs, and she wore a shirt that hung off her shoulder, a bra strap showing itself assertively. She wore high heels, too. Ada thought she was pretty, but not quite as good-looking as William.

“Hey, Miz Liston,” said the girl, and Liston said, “Hello, Karen,” but didn’t look up. William and Karen went upstairs together.

“That door better be open when I come upstairs,” Liston called after them.

When Ada finished her dinner she was not sure where to go. So she very quietly picked up her fork and rinsed it at the sink, and then opened the dishwasher, but she wasn’t certain whether to put it on the top or the bottom. David and she did not have a dishwasher.

“Just leave it in the sink, honey,” said Liston.

When Ada turned around, Liston was looking at her, arms crossed. She glanced at the clock on the wall and back again. It was 9:00 at night.

“Should we try David one more time?” asked Liston, and Ada said yes, gratefully. She had not wanted to be the one to ask. But when she called her home number, no one was there.

“I think I’ll go to bed now,” said Ada. She was not tired, but it seemed the most out-of-the-way thing to do.

“Okay,” said Liston. She put her hands on her hips for a moment and regarded her.

“We’re glad you’re here,” she said, and it made Ada buckle for reasons she couldn’t explain.

“C’mere,” said Liston. She brought Ada to her, and kept her in her arms. Ada had rarely, in her life, been hugged, and she stiffened.

“It’ll be all right,” said Liston. “You’ll be just fine.” She did not, however, say that David would return.

The bedroom Liston put Ada in was decorated in shades of red and blue and green. It contained a small Lego-land that someone had labored over in the corner, and a twin bed with a frame shaped like a racecar.

“This is Matty’s room,” said Liston, “but I’ve thrown him in with Gregory for the night.”

Ada did not like the idea of Matty’s being thrown anywhere because of her, but Liston assured her that he would like it. “He’ll get a kick out of it,” she said. “He’s obsessed with his older brothers.”

“Can I get you anything else?” Liston asked. “A glass of water? The bathroom’s down the hall.”

Ada said that she was fine, and Liston put one hand on her head and looked at her, and told her again that it would be all right. Then she left her alone in Matty’s room.

Liston’s house was built so much like David’s that Ada knew where she was going without asking. She got out her toothbrush and changed into her nightgown. She walked toward the bathroom at one end of the dim upstairs hallway and she passed an open door on her way there. She looked into the room as she did, and inside of it she saw William and Karen kissing on the bed. For one moment, she froze — trying to decide, perhaps, whether to retreat to her room or advance to the bathroom — and she stared. She had never seen a real-life kiss before, and the heads of the parties involved moved about in a surprisingly vigorous way. In the movies Ada had seen, old-fashioned ones that David and she watched together, the heads of the protagonists stayed coolly in place at an elegant angle as they embraced.

Suddenly William looked up and saw her. “What the hell,” he shouted. He stood up and slammed the door.

“Oh my God, Will,” she heard Karen say.

“She came out of nowhere,” she heard William say.

Ada burned with embarrassment. She looked down at her plaid nightgown. It had ruffled wrists and a ruffled hem and was befitting of a much younger child or an old lady. She stood in place and thought about what she had done for a time, and then, afraid that William would fling open the door again, she continued to the bathroom, where she brushed her teeth with her finger and with toothpaste she borrowed from the Listons, having forgotten her own, and then she took her glasses off and splashed cold water on her face and patted it dry with someone else’s towel, which smelled like cologne and was stiffer than it should have been.

After that she walked quickly back to her room, looking straight ahead in case William’s door was open again, and closed the door behind her.

She stood in place for a while, breathing. She was not tired yet, and everyone else was still awake. She stayed up late into the night in Matty’s room, reading one of the seven books that she had brought along with her, and eventually succumbing to the temptation of the hundreds of Legos in a bucket in the corner — they had been her favorite when she was younger, and a favorite of David’s, too — and assembling a little castle with a drawbridge, a king, and a princess.

When, finally, she went to bed, it was difficult to fall asleep. She missed their house and she missed David.

To comfort herself, she imagined the worlds that were orbiting inside of every closed door along the hallway: Matty and Gregory in Gregory’s room, breathing slowly in and out as they drifted toward sleep; and William and Karen kissing violently on William’s bed; and the sheets and towels resting in the linen closet; and the spiders in the basement, spinning their webs, and every small living thing in the house — the dust mites, the gnats; and the water dripping out of the bathroom sink; and below her, Liston, old friend, scratching away at her yellow pad on work for the Steiner Lab, which was their second home.

And she wondered about David, where he might be.

In her mind, she went through the steps of their after-dinner ritual, which began while Ada cleaned up the dishes. Next she would go and stand outside David’s office. His door was always open but a sort of impenetrable field surrounded him if he was working. Since the time she was small she had known the importance of never interrupting him. So she would press her head into the doorframe and stand on the edges of her sneakers and wait, and wait. And then, finally, he would turn to her and smile, as if waking from a dream.

“Let me explain something to you,” he would say.

And then they would sit together at the dining room table and start on a lesson, one of the many thousands that he taught her in her life.

When she asked him a question that he thought was intelligent he slapped one hand down on the table in celebration. “That is exactly the question to ask,” he told her.

When she asked him a question that revealed some chasm in her learning, some gap where a concept should have existed, he put his head in his hands as if trying to summon the energy to explain all that would need to be explained to her to make her fully formed. But he didn’t despair: he started from a point that was more rudimentary than he thought necessary (generally it was, in fact, necessary) and proceeded from there, his graceful geometrical hands drawing diagrams on the pads of paper that he collected from conferences and hotels and then hoarded in his desk. He often said he could not speak without a pen in his hand. He waved with his pen, pointed with it, scribbled absentmindedly when on a telephone call. He drew funny things like flowers and birds when he was talking to Ada, and sometimes during her lessons. For the rest of her life, Ada did this, too. She adopted many of David’s habits. They were alike: everyone said it. And that he understood her — more than anyone else in the world ever understood her — seemed to her like an incredible stroke of luck. “You are more machine than human, Ada,” he said at times. And it was the truth, not an insult. And it was calming to her to be so understood. And, sometimes, she felt it was why he loved her.

She thought of this image as she tried to fall asleep. She pictured herself with David at his desk, the two of them bowing their heads together, their minds a Venn diagram — Ada’s mind full of childish trivia, and David’s full of the mysteries of the universe, and the center between them growing, growing. In these moments he was Zeus to her, and she Athena, springing fully formed from the head of her father, alight with grace and wisdom. There they were at the lab or at home, the two of them, always the two. There they were solving whatever problem it was that she was facing.

In the morning, Ada was woken from a dream about David by the sound of the bedroom door creaking slowly open. There in the doorway stood Matty, holding a canvas tote bag and observing her. She sat up in bed and rubbed her hands over her face.

“I just have to get some stuff out of here,” said Matty, and then he came in and gathered up all of his Lego people and parts, two books, a small portable radio with a trailing wire. All of this he stuffed into his canvas bag, looking sideways at her as he did.

He sidled toward her before he left the room. He said to Ada, “Where’s your dad?”

She lifted her shoulders and lowered them slowly. She kept her face very still.

Then he turned on his heel and closed the door firmly behind him. Ada heard him running down first one and then another flight of stairs, into the basement, she assumed.

Ada rose and tiptoed to the door and put her head out into the hallway. It was a Sunday, and everyone else seemed to be asleep still. As quietly as she could, she descended the stairs and went into the kitchen, where Liston’s work was sprawled out over the table, and a yellow phone was mounted to the wall. She lifted the receiver from its cradle and dialed the number for her and David’s house, holding her breath while the rings came, four in a row, five, ten. Nobody answered.

Then, hanging up the telephone, she pondered her options. It still felt odd to be in Liston’s house for almost the first time after so many years of knowing her. She had no idea about Liston’s habits or her daily routines — no idea, for example, whether she was an early riser on weekends or preferred to sleep late, and no idea what she did when she was not at work and not with David. If Ada had been at home with David, she would have known what to expect from her weekend: David would have stayed in his home office for most of the day, breaking for every meal; Ada would have read or worked on the assignments that David gave her. Some weekends they did something different and interesting: a trip to a nearby mountain for skiing in the winter, for example; or, in the summer, a trip to a cabin in upstate New York that David had been renting since the fifties; or some other excursion to a nearby town or city. Sometimes they went to Washington, D.C.; David had a friend there named George, an artist, one of the few people he had kept in touch with from his childhood. He also went on several work trips a year, to conferences in locations as mundane as Cleveland and as far-flung as Hong Kong. These counted as their vacations: typically they would stay a few extra days in every place, seeing more than they otherwise would have. Sometimes, if he’d be in meetings all day and he thought that Ada would have nothing to do, he went by himself to conferences; on these occasions, he paid the division secretary, Martha, to stay with Ada at the house on Shawmut Way, and returned as quickly as he could. And there were, of course, the yearly trips to New York City, always in winter, always to see the Christmas concert at Calvary Episcopal. On those same trips, they would see an opera or a ballet at Lincoln Center, and visit the Met, and walk in Central Park. David always reserved the same accommodations: two adjacent rooms on the third floor of a bed-and-breakfast in Brooklyn Heights (“Manhattan is overpriced,” he always said, though Ada secretly wondered if he wished to limit, as much as possible, his chances of running into acquaintances from his past), owned by a charming, fragile septuagenarian named Nan Rockwell. She served scones for breakfast and talked with David about classical music until late into the night, playing on her turntable famous recordings that she sought out and traded for like cards. Always, they had dinner at a little cafeteria near Union Square, a nondescript place that David said reminded him of his youth, for reasons he did not explain to Ada.

Ada did not think Liston had any interest in doing these things. She came on most of the work-related trips that Ada and David took, but kept to herself, proclaiming her hatred for hotel rooms and her love of home. In her tastes she was polite but not adventuresome; she hopefully scanned every English-language menu they were presented for its blandest, palest dish. Until yesterday, Ada had always imagined that she did cozy things on weekends, made popcorn, watched movies with her boys, cooked meals with her oldest, Joanie, when she stopped by with the baby. How Ada came up with this idea, she was not certain: she had no reason to believe that the scientifically inclined Liston was domestic in any way. She knew that Liston did not like to cook, and could not abide housework. (She bragged often about raising her boys to be good husbands, assigning the weekly chores on a magnetic whiteboard that she stuck to the refrigerator.) Despite this, she still seemed traditional to Ada, in a way that Ada and David were not, and in a way — if she was honest with herself — that she envied. Liston drank Diet Coke. She brought ham-and-cheese sandwiches to work, on white bread. The sight of them made Ada’s mouth water. The idea of Liston’s house as a bastion of normalcy and tradition, right down the street, was one that Ada had always kept dear: it seemed somehow to anchor her and David’s house physically, in the same way that Liston’s friendship with them proved reassuringly to Ada that there was nothing so unusual about her situation, after all.

It was not until shortly after nine that Ada noticed any movement upstairs. Upon hearing it, she tiptoed to the downstairs bathroom to hide, in case it was one of the boys. She did not want to greet them before their mother was there to protect her.

Ada heard footsteps walking down the stairs and into the kitchen, just as she had done, and then someone picked up the telephone receiver. She could hear it all quite clearly.

“It’s Di,” said Liston, in the other room.

Ada didn’t know whom she had called, but she began to describe to the person the events of the day and night before, beginning with Ada’s phone call to her. Ada froze. She thought perhaps she should clear her throat or turn on the water to let Liston know she was there, but she was immobilized by shyness and fear. She stood still, clutching herself around the middle.

“She’s still at my house. She’s upstairs sleeping,” said Liston.

She paused.

“And what if he’s not back today? When do we call the police?” said Liston.

And then, “He might get in trouble. It might affect Ada. What if they say he’s incompetent?

“It’s a sin,” said Liston. “An honest sin.”

After Liston hung up she began to move around the kitchen, opening cabinets. Ada held her breath. She didn’t think she could emerge, just yet — Liston would know she had heard everything. She decided to wait until Liston went upstairs again, or into a different room, at which point she could make a quick exit and pretend she had been someplace else.

Ada sat down on the closed lid of the toilet. Incompetent, Liston had said. It was the word she had used about David. It contrasted with every understanding of her father that Ada had. She put her face into her hands. And at that moment Liston opened the bathroom door, and shouted in surprise.

She clutched her heart and doubled over. “Ada!” she said. “What on earth.”

“I’m really sorry,” said Ada, not knowing what else to say.

“Are you all right?” Liston asked her, and she nodded.

Liston put her hand to her chin, as if in thought. She was wearing a blue terry robe that looked perhaps a decade old.

“Did you hear me talking on the phone?” she asked Ada, and Ada had the urge to lie, but could not do it. Liston would have known. She nodded once more.

Liston took in a deep breath and exhaled slowly. “I’m sorry, baby,” she said. She opened and closed her mouth, as if deciding whether to say more, and then gestured with her head that Ada should follow her into the kitchen, which she did.

“How’d you sleep?” she asked, and Ada said that the bed was very comfortable, and that she had slept excellently, though it wasn’t true.

“Are you hungry?” Liston asked, and she nodded. On the kitchen counter was a line of boxed cereals, with a gallon of whole milk at the end. “Bowls there, spoons there,” Liston said, pointing.

What David called cereal was hot and eaten with brown sugar. Ada had never before had cold cereal, and she inspected her options carefully, searching for the one that David would be least likely to bring into the house. At last she chose one called Smacks because of the happy frog on the box, one arm extended skyward, proudly presenting its bounty.

While she ate she waited for Liston to speak. She had settled down at the kitchen table, where her papers were still spread out from the night before, and was working out some problem with her pen, as if solving it would help her answer the larger question facing them. Handwritten code blossomed across the page. At that moment a great longing came over Ada for David and for their home. Every so often Liston looked up at her and smiled, but she did not speak: as if waiting for Ada to confess something, some information she had previously kept to herself. But Ada had none.

“Are you going to church today?” Ada asked. She knew that Liston was an active member of the parish just over the bridge, and often on Sundays she had seen Liston marching there and back again with her boys, who were always dressed in ill-fitting khakis, button-down shirts, loose ties, scuffed and poorly knotted shoes. It occurred to her that day that Liston was not dressed for it; she did not wish to be the cause of any change in plans.

“We’ll skip it today,” said Liston, smiling. “The boys will be thrilled.”

She put her pen down then and looked out the window. She spoke without shifting her gaze.

“What have you noticed, Ada?” she said.

“What do you mean?” Ada asked. She hated this: the feeling of being asked to betray David.

“About your dad,” said Liston. “Has he been acting differently? Has he said anything strange?”

“I think he’s just under a lot of stress,” Ada said, and Liston nodded noncommittally.

Both of them were silent, and then both spoke at the same time. Ada said, “I think he’ll be all right.” And Liston said, “Honey. I think we should call the police.”

Ada thought of David’s mistrust of law enforcement; his vehement disapproval of the meddlesome State; his passionate dedication to privacy. And then she decided that whatever fear he had of the police, hers was greater of losing him.

“All right,” she said, and immediately felt unfathomably disloyal, treacherous. She lowered her head.

Ada disliked the two police officers who arrived later that afternoon. She couldn’t help it; her well had been poisoned by David’s mistrust of authority. One was tall and thin; the other short and thin. Both had mustaches.

“And the last time you saw him was?” asked the tall one, Officer Gagnon.

“And has he been acting unusual?” he asked.

“And do you have any idea where he might be?” he asked.

He seemed bored. Both accepted Liston’s offer of coffee, and then sipped it loudly.

“You’re the daughter?” asked the shorter one, finally, and Ada said yes. “And how do you two know each other?” he asked, gesturing back and forth between Liston and her with his pen.

Liston explained, and the two of them looked at each other.

“We’ll have to get social services in here,” said Officer Gagnon. “Since there’s no relation.”

“Really? Are you sure?” said Liston. “I’ve known her since she was born.”

“Sorry, ma’am,” said Gagnon. “Just procedure. They’ll be over soon.”

It was then, for the first time, that Ada let her imagination run its terrifying course. She was an impressionable child, and she thought of what ruins might await her: she had read too much Dickens. Did workhouses still exist?

Before they left, Matty came into the kitchen — the suddenness and quietness of his appearance gave Ada the impression that he had been eavesdropping on them from someplace nearby — and looked shyly at the officers.

“Hey, big guy,” said Gagnon, on his way out.

“Hey,” said Matty, softly, but the door was already closed.

There was little to say for quite some time. Ada sat still at the kitchen table, pretending to read a newspaper, until at last Liston said that it must be close to dinnertime, and stood up, and went to the cupboards. She opened them one at a time, looked inside them beseechingly. At last she pulled down a blue box of spaghetti and some canned tomato sauce and opened both, started a pot of water.

“Are you all right?” Liston asked Ada at one point, and Ada nodded. But the truth was, of course, that she was not — would not be until David had returned. If he returns at all, she thought, and put her chin in her hands to keep it from trembling.

She stood up from the table abruptly. She had never cried in front of Liston before, and she didn’t wish to now.

“I think I should get a few more clothes from my house,” said Ada, and walked quickly out the door before Liston could follow her, or agree.

She inhaled deeply, willing herself to calm down. Outside it was beautiful. It had cooled off slightly for the first time that August. In the distance the low hum of a lawn mower started. One of the neighbors was barbecuing. The smell of burning charcoal and meat, the particulates of matter that found their way to her on a pleasant breeze, normally signaled happiness and relaxation to Ada. Ever since learning about neurotransmitters from David, she had imagined her brain as a water park, a maze of waterslides down which various chemicals were released. Charcoal and smoke and fresh-cut grass usually sent rivers of serotonin down the slides in Ada’s head, as she pictured them. But that night the scents only served to remind her of David’s absence. Warm summer evenings, he always said, were his favorites, too.

Ada let herself in through the kitchen door and poured a glass of water from the tap. She took it with her to her room at the top of the stairs and gazed out the window, and then felt drawn to the old computer at her little desk. She turned it on. She dialed into the ELIXIR program. She began to type. There was something comforting in the familiarity of ELIXIR’s responses, the small turns of phrase she recognized as having come from colleagues at the lab. Where is David? she typed, and ELIXIR said, That’s really a very good question. An answer that reminded her, in fact, of David’s syntax.

There was a great deal to tell ELIXIR. It had only been two days since their last conversation, but it felt like it had been much longer. She looked at the clock after twenty minutes and, fearing that Liston would worry, shut down the program and then the computer, which gave a long sweet sigh as it went to sleep.

It was then that she thought she heard someone moving downstairs. She held her breath, listened for several more seconds.

A drawer opened someplace deep in the house. The basement, she thought. Footsteps. Someone dropped something on the floor. Someone began to walk up the basement stairs.

Ada was easily frightened as a child and she sat frozen in place, clutching her water glass, terrified to move. She eyed the window, measuring whether she could jump out of it if necessary. She decided, at last, that the thing to do was to ascertain the identity of the other person in the house as quickly as possible, so that — if necessary — she could make her escape.

“David?” she called out, loudly, bravely.

There was no answer. She tensed, prepared to run.

“David?” she called again.

“Hello,” said David, his voice warm and familiar. “Is that you, Ada?”

She went limp. All of her muscles contracted and then relaxed. She had not realized the weight of the fear she had been holding in her gut, the tension of it; she felt as if she were breathing out completely for the first time in her life. Her face was crumpled and red when she descended the stairs and met her father in the kitchen. He paused with a hand on the wall. He was holding a notepad in his other hand and he had one of his contraptions, which looked something like ski goggles, pushed back on his head.

“Good grief,” said David. “What’s the matter, Ada?” The look he wore was a sort of perplexed smile, as if they were about to discover a grand misunderstanding that they would look back on one day and find comical.

“Where have you been,” she lamented. “Where did you go?”

Her voice must have conveyed a very particular emotion — it was anger at David’s betrayal of her trust. From the time she was small, she had felt it whenever she was embarrassed in public, with him by her side: while skiing, for example, if she fell down and, in the tangle of her equipment, could not immediately get up. “Help me,” she would mutter to David, under her breath. She always sensed, somehow, that it was his fault she had fallen down. She felt the weight of others’ stares upon her, seethed in her own embarrassment, converted it into anger at her father. He seemed so well equipped to deal with anything, so utterly competent: and this made her feel that it was his responsibility to preempt and prevent any mistake, any humiliation, not just for himself but for her. Standing in the kitchen, staring at her prodigal father, she felt the same emotion, only stronger: thinking of what she would have to tell Liston, what Liston would invariably tell her boys. In that moment, Ada knew for the first time she could no longer hope to protect David from Liston’s judgment, from anyone’s judgment — as she had been doing, if she was honest with herself, for over a year.

David had not answered her yet. He was looking at her in a hazy, puzzled way.

“David,” she said again.

“I told you,” he said finally, speaking carefully, measuring his words. “I told you I was going out of town for work.”

As an adult, when Ada tried to recall her father’s face, it was often and regrettably this version of him that she thought of: David looking mad, ski goggles pushed back on his head, his shirtsleeves rolled up. There was little connection to David as he normally was, placid, reserved, attentive. This David was growing increasingly stubborn with every additional question he was asked. He had been in New York City, he said, meeting with the chair of the Computer Science Department at NYU. Ada tried to convince him to come back with her to Liston’s, but he wouldn’t.

She studied him for a moment.

“Really, this is silly, Ada,” he told her. “A simple misunderstanding. I’m in the middle of an experiment.” He held forth the notepad he was carrying as if by way of explanation. Pointed to the device on his head.

“Wait right here, then,” said Ada, and she ran to get Liston.

Inside Liston’s house, Liston was pouring the pasta into a colander in the sink. Steam rose up from the boiling water and wilted her hair.

“He’s back,” Ada told her. “He says he was out of town for work. He says he told me. Maybe I forgot.”

It pained her to say it.

Liston looked at Ada uncomprehendingly for a moment and then followed her out the door, down the street to her house. By the time they reached David, he was back in the basement, bent over the device he had been wearing, turning into place a tiny screw.

“Shhhhhhhh,” he said, as Liston began to speak.

“Honestly, David,” said Liston. “Enough of this.”

He straightened and then looked wounded.

“You’ve been gone for almost forty-eight hours,” said Liston. “Where were you?”

“I was in New York for work,” he said slowly. “For heaven’s sake. I wasn’t gone long at all.” But his face was changing.

“What work?” she asked him.

He looked down at the workbench. Spun the device on the table in a full circle.

Liston folded her arms.

“It’s time to tell Ada,” said Liston. “David? Do you hear me?”

They brought Ada to the living room to deliver the news. Later, she recalled wondering, perversely, if this was what it was like to have both a father and a mother. They sat together across from her. She was on a little chair that David said had come from his grandmother. They were on a leather sofa that David attended to from time to time with an oil that smelled like lemons.

David looked at Liston for help, but she shook her head.

He cleared his throat.

“Two years ago,” he began, “at Liston’s insistence, I visited a doctor for the first time in quite a while. There I was instructed to return for further testing. Upon doing so, I was informed that it was likely that I might be in the early stages of Alzheimer’s disease. I disagreed with that assessment. I still do.”

He paused.

“How familiar are you with Alzheimer’s disease?” he asked.

Ada considered, and then said she knew what it was. She had read about it in some book or other, or perhaps more than one book. It was part of her vocabulary. She pictured it as a slow gray fog that rolled in over one’s memory. She pictured it seeping in through the doors and windows as they spoke, invading the room. She felt cold.

“Have you been back to the doctor since then?” Ada asked.

Liston glared at David.

“No,” he said, hesitantly.

“What?” he said to Liston. “There’s nothing they can do for me. Even if their diagnosis is correct.”

“You seem fine,” Ada said to him, and to Liston, and to herself.

“I am,” he said. “Don’t worry too much about this, Ada,” he said. “I’m quite all right.”

Ada could feel the tension between David and Liston. She knew, though she was young, what was causing it: it was Liston’s wish to protect her with honesty, and David’s to protect her — and himself — with optimism, wishfulness, some willful ignorance of his impending fate.

“I think David might have told me he’d be going out of town, actually,” said Ada. “I can’t remember now.”

It was a lie. Of course it was a lie. Liston looked at her sadly.

“You see?” said David, but Liston didn’t respond.

Finally, in the midst of their silence, Ada stood up. She turned to Liston.

“I guess I can stay here now,” she said, and she excused herself, and walked slowly up the stairs to her bedroom, which was as unfrilled and austere as a man’s, wallpapered in a brown plaid that the previous owners had chosen. She’d been reading The Way of a Pilgrim, like Franny Glass, and although she was not religious, she said the Jesus Prayer aloud, quietly, five times. She told herself that everything would be fine, because she could imagine no alternative. Because no life existed for her outside of David.

In a week, the Boston Department of Children & Families came to visit them. Liston had called Officer Gagnon to let him know that David had been found, but they were concerned enough about his disappearance to investigate.

David was appalled. He sulked his way through the home visit, with a woman named Regina O’Brien, a gray lady with gray hair. To her questions he gave single-word answers, sometimes unsubtly rolling his eyes. In order to offer an explanation for an absence that had brought the police to their home, David was forced to reveal his diagnosis to the DCF. His first proposal that he had simply forgotten to tell Ada that he’d been going out of town had seemed to alarm them more than it assured them of his competence.

Then came a question that David and Ada had not prepared for in advance. Miss O’Brien looked at Ada and asked how she was doing in school.

Ada paused. She looked at David, who looked at Miss O’Brien and told her that Ada was doing very well in school.

It was not, perhaps, a lie, if one counted David’s method of educating her at his laboratory as school. He had always been hazy about homeschooling Ada; in that decade, everyone thought it was odd and eccentric, but not out of line with the rest of David’s odd, eccentric behavior. Everyone, including Ada, seemed to accept that he had worked something out with the state. In that moment, for the first time, it occurred to Ada that perhaps he never had.

It must have occurred to Regina O’Brien, too, for she looked at Ada levelly and asked her what school she attended.

She panicked. She looked at David, who said nothing. She thought she should lie. “Woodrow Wilson,” she said, naming a nearby middle school, uncertain whether it was even the one she’d be sent to.

“And what grade are you in?” asked Miss O’Brien.

“Eighth,” said Ada.

Miss O’Brien paused.

“And who’s your favorite teacher there?” she asked.

At last, David interjected. “She doesn’t go anyplace. I teach her,” he said. “I provide an education for her at home and at my place of work.”

And from the look on Miss O’Brien’s face, Ada knew that they were deeply in trouble.

Later in the 1980s, a series of cases worked their way through the Massachusetts courts that would define the laws that now govern the idea of homeschooling. In Care and Protection of Charles & Others, one will find an overview of what is now required of homeschoolers in the state of Massachusetts: Prior approval from the superintendent and school board, for one. Access to textbooks and resources that public school children use, for another. David and Ada had neither. In 1984, David’s failure to enroll his daughter in any school was only further evidence of his neglect, in the eyes of the DCF.

He seemed not to recognize the severity of the allegations against him. He felt it was impossible that they could take his child from him. Absurd. He told Liston it would not happen.

But after that first visit, their lives began to change. The DCF commanded David to enroll Ada in an accredited school. Miss O’Brien recommended to her supervisor that home visits be continued, and social services required David to see a doctor regularly to monitor the progress of his disease. To see whether, and how fast, he was progressing toward parental incompetence. Incompetence: the word that Liston had once used in reference to him. Incompetence: the opposite, to Ada, of her father’s name.

The Queen of Angels School was a brown brick building, four stories high, set close to the sidewalk. One wide short flight of stairs led to six unpretty industrial doors, painted a dull dark blue. Its roof, surrounded by high chain-link fences on all sides, was used for gym class in warm weather. Its lower windows had metal bars running from top to bottom — added several decades after the school was first built, an attempt to calm paranoid parents who increasingly saw Dorchester as a place to be feared — and its upper windows were narrower and more numerous than what would have been standard for the building, which gave it the look of a medieval fortress or a city wall.

On a Wednesday in September, more than a week after the school year had begun for everyone else, Ada walked for the first time into the Queen of Angels Lower School. Liston and David were with her; all three had taken the day off of work. For the weeks following the DCF’s visit, there had been a debate. David had wanted to enroll her in the local public junior high, but Liston had insisted that that would not do. So, grumblingly, David and Ada and Liston had gone at the start of the month to meet with Sister Aloysius, the principal, and Mr. Hanover, the president, both of whom were in charge of welcoming new students into their fold.

In the high-ceilinged office occupied by the latter, the three of them sat and listened to a speech about the benefits of a Catholic education, the moral enlightenment Ada would receive, the community provided by the school. David leaned forward in his chair, his elbows on his knees, looking down at the floor, the top of his bald head catching light from the window and shining. He sat up, stretched his arms and legs uncomfortably, sighed out heavily once or twice. Liston glared at him. Ada hoped that no one else noticed.

The two administrators were tactful about her history, referring to her homeschooling only vaguely, euphemistically, as if it might behoove everyone to forget about it entirely. Ada assumed that Liston, who was well known in the Queen of Angels parish and active in the school, had prepped them thoroughly.

Ada listened attentively to everything that was said, looking around with interest at the decorations and the architecture: the crucifixes on the walls, above all the doors; the ancient, ticking clocks in metal cages; the colors of the school, which had most likely been redone in the previous decade and consisted mainly of muted, modernist tones. Pea-green, goldenrod, maroon. She felt in certain ways that she had breached a castle wall; she had so often walked past Queen of Angels and scanned its exterior for signs of what it must be like inside. As outsiders, David and Ada had always been only hazily aware of the ways in which Dorchester was divided, though it interested David, and he often asked Liston to describe it. To Liston, to her children and friends, one’s parish was more important than one’s neighborhood or one’s street. The first floor of Queen of Angels contained the local parish school, a grammar school, perhaps two hundred students in sum from kindergarten through eighth grade. But the upper floors contained a central diocesan high school that drew from seven different parochial schools, including the one beneath it, and so beginning in the ninth grade the school widened into a river of students from a broader swath of Dorchester, and some from the city beyond. Nearly everyone in Savin Hill, including all three Liston boys, attended Queen of Angels: Matty and Gregory in the Lower School, William in the Upper. Liston herself had gone there for her entire education as a girl. This was the only fact about the school that David found at all reassuring. “Well, I suppose it did all right by Liston,” he said to Ada, but a note of skepticism still made its way into his voice. Ada would enter as an eighth-grader, based on her age and not much else, and be placed among students who had known each other for years. But Sister Aloysius assured her that by ninth grade she would blend right in.

At one point, she leaned in toward Ada kindly and put a hand on the desk. “Ada, dear,” she said, “if ever you find yourself unable to grasp something, or falling behind in a course, don’t hesitate to come to me for help.”

At this David’s head jerked to attention and, finally, he spoke. “There is no question that Ada will be able to grasp what you put before her,” he said, a sort of quiet viciousness making its way into his voice. “In fact, I’d go so far as to say she’ll throttle it. The question is whether you’ll be able to provide my daughter with the sort of material that will offer her even the slightest challenge. Or do you,” he said. “Or do you,” he said again, and then he lost his words.

All of them, including David, fell for a moment into silence.

“I can guarantee you, sir,” began Mr. Hanover, at the same time that Liston stood up and thanked them for their time.

“Do you have any questions?” asked Sister Aloysius, looking only at Ada, and Ada shook her head quickly in response.

Later that day, Liston called to ask whether Ada would like her boys to walk her to school in the morning. She declined, not wanting to saddle them with her, feeling sure that the request would be a burden to them. The recent turmoil in her life had momentarily supplanted her crush on William as the place her thoughts wandered when left undirected. She realized that she had not daydreamed about him for a week.

In the evening, David mustered up some energy and made them both dinner. “Whatever you like, Ada,” he said. She had chosen pot au feu, a special favorite of hers that David made only on occasion, and went with him to the butcher on Dot Ave to pick up the beef.

She let him amble ahead of her and concentrated on his walk, memorizing it, wondering what it would be like to be without him. For the past several weeks she had been investigating Alzheimer’s disease on her own, with the help of the scholarly library at the Bit. She had discovered two things: first, that the disease typically moved at a fairly sedate pace. Life expectancy, in that decade, was thought to be about eight to ten years from diagnosis. But it had been over two years already since he was first forced by Liston to see a doctor, and — if Ada was honest with herself — she had been noticing symptoms of forgetfulness for longer than that. She had been convincing herself for years that David had always been absentminded.

The second bit of information that she learned, more troublingly, was that when the disease was diagnosed in younger people, its progression was often more rapid. David was fifty-nine: well below the age the literature listed as the cutoff point between early-onset Alzheimer’s and the more typical variety. And in early-onset patients, the disease could move quite fast: two or three years until the individual’s comprehension skills were entirely lost, until the individual was no longer verbal. After that, quite rapidly, the function of his muscles and all of his reflexes would shut down completely.

Ada had squeezed her eyes shut against this possibility. She told herself it would not happen: that David would be the exception.

The butcher shop was busy with customers, but the owner knew and loved her father.

“What can I get you, Professor?” he asked — his perpetual name for David, and for anyone in the neighborhood who manifested signs of formal education — and David, leaning forward, his hands behind his back, selected his cut of beef carefully, brought it home, cooked it up for Ada while she sat in the kitchen and talked to him, her father, her best and most important ally in the world.

“I’ll tell you something, Ada,” said David. He turned to look at her, pushed his glasses, steamy from the pot of water he had boiling on the stove, back up on his nose. “It’s going to be a different lab without you there. Quite a different lab altogether,” he said. “I know Liston’s really going to miss you.”

“I’ll miss her, too,” said Ada. She was talking, of course, about her father; just as he was talking about her.

Their old and comfortable house filled up with the smell of herbs and onions and garlic. And Ada thought in that moment that it might not all be so bad.

Liston had warned her not to be late, so before she went to bed Ada had consulted the schedule she’d received, noting the start time of all the classes. Her first was at 8:00 a.m., and she planned on arriving at 7:50 just to be safe.

At breakfast, David was quiet. He did not know what to say to her: she could tell that he felt he had failed her.

Then he asked, as if it had just occurred to him, what she would use to carry her books, and she pointed to a canvas bag on the floor that she had scavenged from the basement.

“Oh, dear,” said David. “That won’t do the trick. Wait here,” he said, and he went into his office and emerged, proudly, with a brown briefcase that unlocked only when a five-digit code was entered mechanically onto a rotating combination lock. David had not used it in years, but it had been an object of fascination for Ada when she was small. He had programmed the lock with a number he promised she could guess. As a smaller child she had spent hours entering guessable numbers: her birth date, then her birth date backward; his birth date, forward and backward; the address of their house with three zeroes in front of it. But she’d never guessed correctly. Every now and then, still, she walked into his office and idly tried a new idea.

“It’s yours,” he said to her proudly.

She took it from him. She was pleased: she felt professional, suddenly, like her own person.

“You’ve never guessed the code?” he asked.

Ada shook her head.

“It’s just code. The word code, using alphanumeric substitution,” he said happily. “No shifts. Stupidly simple. The sort of password that longs to be cracked.”

Ada had, long ago, memorized a table that listed each letter next to its corresponding number, 1 through 26. She turned the dials on the combination lock—3 for C, 15 for O—until they read 31545, and then pressed two buttons to its right and left, and the latches opened with a satisfying, muted pop.

Inside, the briefcase was empty, lined with a silk material that was yellowing in places. One half of the briefcase bore little elasticized compartments meant to hold writing implements and notepads, and David now took a pen from his shirt pocket and tucked it into place inside one. He walked back into his office and came out again holding an unlined pad of white paper, stationery from the Steiner Lab that David had ordered en masse five years ago. He handed this to Ada as well.

“There,” he said. “Now you’re all ready.”

“Shall I walk you to school?” he asked her.

“I’ll be okay,” said Ada. In fact she would have liked him to, but she wanted to demonstrate to him that she’d be all right — to show him that she was grown up now, to lessen his guilt, which, that month, had manifested itself in ways that Ada had begun to notice. He looked at her for longer than usual; he asked her more often what she’d like to do in the evening or on weekends. A dark shadow crossed his brow now whenever he could not locate a word or phrase, which happened many times each day. The night before, in the middle of a glass of sherry, he had apologized to her.

“I should not have put you in the position in which you now find yourself,” said David. “I was trying to do what I thought was right, but I fear I’ve made everything worse.”

“I’ll be all right,” Ada had said, reassuringly.

“Oh, my dear. I feel as if I’m throwing you to the wolves,” said David. “Genuflecting to the cross. Learning the rosary. Confessing your sins to Father So-and-So. Good heavens,” he said.

He took a pensive sip.

“Sometimes I still think I should have sent you to public school,” he said. “But Liston knows best, I suppose.”

He had packed both of them lunches the night before, as he often did, but that day, for the first time, Ada would be taking hers separately. Carrying it herself. She put the brown bag inside her briefcase, squashing it slightly when she closed it, feeling the give of the bread. They walked together over the bridge and then, at the main intersection that followed, Ada turned left and David turned right.

“What is it that I tell you here?” asked David. “Have a good day, I suppose?”

His face looked pinched, slightly red around the nose. Ada stood apart from him: she did not know how to comfort him. She needed comforting herself.

He looked at her ruefully. “Don’t take them too seriously,” he said finally. “Don’t take anything too much to heart, Ada. All right?”

She nodded solemnly. And then she watched her father as he walked away, carrying his own briefcase down by his side. She longed in that moment to go with him: to run after him, to sigh deeply and contentedly as she settled into her work at the lab. Instead she turned, finally, and walked in the opposite direction. Her head was down, like David’s head. From above, they would have looked like mirror images of one another, one larger, one smaller: a Rorschach test; a paper snowflake, unfolded; two noblemen pacing away from one another in preparation for a duel.

It was a short walk to Queen of Angels from there. She tightened her right hand around the handle of the briefcase; it made her feel professional, secure, as if she were clasping her father’s hand. When she arrived, she found she was alone. No other students were in sight; and the first-floor windows were too high to see inside from street level. Ada walked up the steps, feeling increasingly ill at ease. At the top of them, she tried the handle of a door and found that it was locked. She tried another. Locked. She stood for a moment outside, wondering about her next move; a large part of her wanted to turn and walk home. I tried, she imagined saying. The door was locked. She did not feel yet that she had any obligation to the school; she did not feel, yet, that she lacked agency, or the right of self-governance. In her life, Ada had rarely been told that she could not do something she wished to do, because all of her desires aligned so completely with the desires of those around her, because her deference to her father and all of his colleagues meant that her requests were usually very reasonable and very small. All of her life she had operated in the world of adults, and the world of adults had welcomed her.

Now she decided that it was reasonable that she turn and walk home, but as she reached the bottom of the steps, one of the dark blue doors opened behind her and a low voice issued forth.

“Where do you think you’re going?” said the voice.

Ada turned around. The man in the doorway was small and stern. He had gray hair parted sharply to the side of his head, and brown pants, and a wide, short, brown tie.

“Nowhere,” she said. She was surprised into saying it.

“Were you leaving?” the man asked.

“I was trying to get in,” said Ada. “The door was locked.”

“And knocking is something you’re not familiar with?” he asked her. She had never been spoken to in this way, so harshly.

“I’m new,” said Ada, by way of explanation. She began to dig in the pockets of her skirt for her schedule so she could show him, but the man was already coming toward her. Shockingly, he took her by her elbow. She had not ever been handled in this way. He brought her forward, up the steps, pushing her ahead of him as if she might try to escape. And once she was inside he pulled the door closed behind her with a crack.

It was explained to her by the secretary, when she reached the office, that although her first class began at 8:00 a.m., homeroom was at 7:40 sharp. The front doors were closed and locked at 7:38 a.m. exactly, and after that students were required to ring a bell to be let in, and their lateness was noted on their record. Ada was certain that this had not been explained to her on her first and only visit to the school, but it felt futile to protest — they were so certain of her guilt that it seemed better, more effective, to hang her head and nod.

The secretary, Mrs. Duggan, donned her half-moon reading glasses to take a look at the schedule that she still held in both of her hands. She glanced up at the clock on the wall.

“8:01,” she said. “You should be in Sister Margaret’s class right now.” And she walked Ada out of the office, down a short hallway, around a corner.

“If you’d gone to your homeroom you would have gotten your locker assignment. But we should get you to class now. You’ll get it tomorrow,” said Mrs. Duggan.

Although it hadn’t occurred to her yesterday, Ada now noticed the smell of the place — the famous schoolhouse smell she had read about in many of her favorite books. Chalk and soap and dust and metal. She took it in. Overhead, fluorescent lights flickered from time to time distractingly.

She reached Sister Margaret’s classroom, and Mrs. Duggan turned to her.

“I’ll introduce you to your student ambassador first,” she said. “You were supposed to meet her this morning.”

She opened the door and popped her head inside. “Sister,” she said, “could I borrow Melanie McCarthy for a moment?”

After a pause, a girl emerged from the classroom and into the hallway. She looked at Ada unblinkingly. She was beautiful: the sort of girl that Ada suddenly and irreversibly realized she wanted to look like. It had never really occurred to her to want to look any particular way before. Melanie had very fair blond hair that fell back and away from her face, held there by what seemed like a permanent breeze. She had smooth unblemished skin — Ada had noticed that lately her own had been less cooperative — that was tan still from the summer. Ada imagined she spent a great deal of time lying on a beach someplace, or performing some wholesome athletic activity like field hockey. Her skirt fit her perfectly and fell to the tops of her kneecaps, which themselves were perfect. Her white socks were pulled to the top of her shins and folded over precisely. Ada was wearing ankle socks, scrunched down by her shoes, because she had nothing else to wear.

“Ada, this is Melanie,” said Mrs. Duggan. “She’ll be your ambassador here at Queen of Angels.” And Ada could tell by the way she looked at Melanie that here was a girl she approved of, a tidy girl with brushed hair and a family who donated the correct amount each year. The name of the school seemed, in that moment, to apply to Melanie herself. Ada extended her hand ever so slightly, the way she would have upon being introduced to a graduate student, and then retracted it. A handshake was not correct.

“She’s in Group B with you, so she has the same schedule you do. If you have any questions,” said Mrs. Duggan, “she’s the one to ask.”

Melanie said nothing. She smiled, briefly, and looked at Ada inquisitively. She was Ada’s height exactly and their eyes met quickly before Melanie turned them away, back to Mrs. Duggan, who was thanking her for her kindness. “And I’m sure Ada will thank you, too,” she added. “Won’t you, dear?”

She nodded.

Mrs. Duggan rapped on the glass once with her knuckles and then opened the door. Sister Margaret, inside, was poised with her hand at the chalkboard, about to finalize some equation. Mrs. Duggan put a hand on Ada’s shoulder and ushered her into the classroom. Melanie trailed behind, and then walked gracefully back to her desk and, sitting, tucked one leg behind the other.

“Sister Margaret,” said Mrs. Duggan. “Class. This is Ada Sibelius. She’s new here. Ada, why don’t you tell the class a little about yourself.” She and the hallway monitor had both pronounced her last name incorrectly — something like Sibellus — but Ada knew not to correct them. David would have. She had never been certain about how she’d acquired the few social skills that she possessed, which had always acted as a balance to David’s lack thereof. Genes, perhaps — the genes of the surrogate mother who gave birth to her. Or her interactions with the other members of the lab. Either way, Ada called upon them not to fail her in that moment — to produce the right response, the right introduction.

She looked out into the sea of maroon-and-navy-clad eighth-graders, boys and girls all returning her gaze impassively. She held her briefcase in her right hand and curled her first around its handle more tightly as she struggled to bring words — any words at all — to mind. She dug her nails into her palms. Anything she could imagine saying felt too far-fetched, too bizarre. I’ve never been in a school before, she could say. My name is Ada Sibelius and my favorite mathematician is Gauss.

Finally she settled on Hi. “Hi,” she said. “I’m Ada. I’m thirteen. I’m from Dorchester.”

Which was, of course, silly. They all were.

The math class was incredibly basic. Ada had had a suspicion it would be, but it was so simple that it was actually interesting to watch, at least at first: Sister Margaret was spending time on the multiplication of fractions, teaching the class in a slow, methodical way, drawing Xs from top to bottom and bottom to top. Ada knew to do this, intuitively, but it had never been mapped out for her in that way, mechanically. Everything she knew of math was somehow more fluid, more instinctual, than the diagrams that Sister Margaret was putting on the board. It felt like someone telling her how to speak, or by what method to put together an intelligible sentence. It felt like someone telling her how to access a memory. How to breathe.

And yet, all around her, students were completing exercises given to them by Sister Margaret, using the same cross-hatching technique she was demonstrating at the front of the room. She wrote a list of equations on the board and then roamed the room silently as students put their heads down to work at the task. Ada put her briefcase atop her desk and carefully turned the dials into place and sprang the latches with a louder pop than she’d recalled. Several students around her turned to look, and it was then that she noticed the backpacks that were tucked neatly into baskets beneath each student’s seat: red and green and blue canvas bags with straps, the sort David called satchels. Instantly, her face colored, and she lifted and lowered the lid of her briefcase as quickly as she could, retrieving from it the pad of Steiner Laboratory stationery and the pen her father had tucked into place that morning. Then she pushed the briefcase under her desk.

She began to work. After a moment she felt a presence over her right shoulder, a shadow on the desk.

“In this class we use pencils,” said Sister Margaret, more loudly than Ada thought necessary. “And graphing paper.”

Ada looked up at her. She hovered there disapprovingly, her small mouth turned downward, her hands folded before her. How was I supposed to know this? Ada wanted to ask her. It was a question that had occurred to Ada perhaps ten times that day already. How was I supposed to know any of this? She felt anger toward her father and Liston in equal measure. Surely, Ada thought, they could have prepared her better than this.

A sharp bell signaled the end of the period, and Ada took out her paper schedule to see what was next. English, then history, then physical education, then lunch, then home economics, then something called general science. She wondered what it might be — what they might plan on teaching her in a science course with no specialization.

When she looked up again, she realized that every other student, including her ambassador, had left, and new students were coming into the classroom. She scurried out into the hallway and caught a glimpse, at the end of it, of Melanie McCarthy’s bright blond hair, her bright white knee socks as they disappeared around a corner. She ran to catch up, to follow the class to its next destination.

“No running!” came the reprimand from an unknown voice behind her, and she broke her gait, but felt a sort of panic rising inside her. She did not know where A-Hall was. Furthermore, she felt certain that she would cry if she had to ask anyone for help. She thought of her father, how easily he approached strangers, how little hesitation he had when it came to asking for what he needed. She wondered, for the first time, what he had been like in school. She had never once thought to ask him about it — perhaps because she had no experiences of her own to compare his to — but now she wished she had. Instinctively, she knew that it would be a mistake to talk to anyone.

She tucked her briefcase under her right arm and held it tightly there; it felt less conspicuous that way than it did while swinging in her hand. At last she reached the end of the hallway, and turned right. Thirty feet ahead, the rest of her class marched or skipped or slung arms familiarly about each other in a way that made her understand that they had moved through their entire education as one unit: that they knew each other’s parents, that they had gone to each other’s houses for sleepovers. That they played sports together, in and out of school. That they knew each other’s embarrassments and victories, and that they had come to terms with all of them, had settled comfortably into groups and clusters and strata that it would take Ada years and years to accurately map.

She was the last to arrive in her next class, and in all of her classes for the rest of the day. She gained a new textbook in every class, was instructed by every teacher to cover it in brown paper before the next day. They were bulky, these textbooks; she could fit only one in her briefcase. The rest she carried in the crook of one arm, wishing fruitlessly for the use of her other one.

At lunchtime she walked into the cafeteria and froze: it was then that she realized the extent of the stratification of the Lower School, the broad and awkward age range, from five-year-old kindergarteners to thirteen-year-old eighth-graders, some of whom looked as if they might as well be teachers. And within those ages, the boys and girls divided themselves; and within the two genders, they all seemed somehow divided by levels of attractiveness or confidence. She hovered for a moment and then plunged forward, as if into cold water. Briefly, wildly, she scanned the room and saw the angelic head of Melanie McCarthy, wondered if she should approach her, as the only other student she had formally met. But Melanie was surrounded by other girls sitting shoulder-to-shoulder on both long benches, as close and tight as matchsticks in a box.

Ada found the only empty table she could find, knowing somehow that it was not hers to take, that it belonged to a group that would very likely claim it in a moment. But she had no other options. She sat at the very end of it and took from her briefcase the paper bag that David had handed her that morning, its contents now squashed. After a few moments, the other half of the long table began to fill with boys who looked her age or slightly younger. None of them had been in her morning classes. Seventh-graders, maybe.

“Nice briefcase,” one of them said, with so much force that she imagined everyone in the cafeteria had heard. Ada glanced over quickly but could not determine which boy it had been. The little group bent forward and backward, felled by their own laughter. She was holding her sandwich halfway to her mouth, and she stiffened there, uncertain how to proceed. She felt endlessly observed. She lowered the sandwich and followed it with her eyes. She had never been so directly targeted before — once or twice she’d been shouted at by another child on a walk to or from the store, or while going someplace else in the neighborhood — but on those occasions there was always the possibility of disappearance, of walking quickly in the opposite direction, pretending she hadn’t heard. Here she was a stationary target, a sitting duck. She froze, still as a deer, keeping her eyes down, waiting for the tide of humiliation to wash over her and recede.

“Nice briefcase!” the boy shouted once more, having successfully elicited a laugh from his friends the first time, and Ada saw then that it was a ruddy, freckled boy, quite small for his age. He looked back at her. “Yeah, you!” he said. “I said I like your briefcase. Aren’t you gonna say thanks?”

Later, when she thought it likely that interest in her had faded, she stood up as quickly as she could, tucked her now-hateful briefcase once more under one arm, her textbooks under the other, and asked the only adult she could find where the bathroom was. Then she walked down the hallway, opened the bathroom door, and, upon finding it empty, tucked herself into a stall. She set down her stack of textbooks and her briefcase on the floor. A wave of relief washed over her, to be unseen, hidden inside something small. To be totally alone.

She stayed there for twenty minutes, checking the digital wristwatch that David had given her, waiting for the bell. She looked at her schedule. She would not be late again. Girls came into and out of the bathroom, holding forth on various subjects in rushed, enthusiastic bursts of language that Ada sometimes didn’t understand. She noted their diction with interest, sentence structures she had never heard before, expressions she had only heard in restaurants or on the T. The 1980s marked the dawn of like as a sort of linguistic master key, a shapeless bendable word that fit into the crevices of sentences as perfectly as honey. The girls at Queen of Angels poured it over their speech greedily, and Ada mouthed it herself, in her bathroom stall, practicing along with them as she often did with other members of the lab.

At 11:54, when the bathroom was empty, Ada opened her briefcase on her lap. From it she took the pen, the pad of paper, one textbook, and added them to the pile of textbooks she’d made on the floor. Then she tucked the empty briefcase into the nook between the toilet and the wall. She’d leave it there for the rest of the day. Her books didn’t fit into it anyway. She let herself out of the stall and into the hallway once more, carrying her textbooks on her meager hip, and she walked to her next class.

At the end of the day, when she returned to the bathroom nearest the cafeteria, she found that the briefcase was gone. She opened every stall door to make sure. She stood for a while, pondering what to do, wondering how she would explain it to David. In the mirror, she looked unlike herself.

The foyer of the Lower School was crowded with children, all jostling against one another to exit. Outside, she saw in her path a group of older boys from the Upper School — some of them so much older that they seemed to her like men, the whole broad-shouldered bunch. They were standing in a group, some of them leaning against the wall of the school, others standing splay-ankled in the middle of the sidewalk. Groups of boys terrified her beyond all measure; typically, if she saw them ahead of her on any walk, she crossed the street to avoid intersecting with them. But she had turned left out of the school doors, and the street was too busy to cross, and to turn around completely would have made her too visible.

She continued, head down, hoping to pass them unnoticed, when she heard her name.

“Ada,” said one of them — she still had her eyes on the ground, and her instinct, really, was to keep going. But then he said it louder.

She was past them already. She clutched her books more tightly to her chest and pivoted slowly on a heel. She could feel a deep, defeating warmth spreading downward from her scalp. She looked up at William Liston.

“Hi,” she said — so quietly that she might as well have mouthed it.

“How was your first day?” The other boys looked at her or away. Two of them continued whatever conversation they were having, uninterested.

“Okay,” she said, trying to produce more volume this time, wondering what anyone else would do or say at this moment. Make a joke, perhaps: some tossed-off line, some little act of self-deprecation or school-deprecation that showed him she belonged.

William Liston paused, as if waiting for more.

“Cool,” he said finally, and then turned back to his group. She understood that she was dismissed. She also understood that something further had been expected of her, a few more conversational twists and turns, and she racked her brain for anything, another word, another phrase, but she was not a native speaker of William’s language, of the language of children.

Suddenly, from behind her, she heard her name again.

“Ada! There you are!” called a voice she recognized instantly as her father’s. She froze.

“And William Liston!” he added. Ada turned around slowly, nervously, and saw David on the opposite sidewalk, wearing the large glasses that had gone out of fashion half a decade before, one half of the collar of his shirt tucked in on itself messily. He did not look to the right before bounding out into the street, and the driver of the car that screeched to a halt in front of him rolled down the car’s window to object.

“All right, all right,” said David, holding up a firm hand in the driver’s direction. “Let’s not overreact.”

Ada had told him she would meet him at the lab after school. It had not been the plan for him to come here. All around her, she could hear a ceasing of conversation as her classmates stopped to watch the spectacle of David, his clothing flapping in ways she had never before noticed, his thin frame jangling along, elbows sticking out at odd angles.

He reached the sidewalk and waved brightly to William, calling out his name once more, telling him hello.

“Hey,” said William. One of his friends turned his back to all of them, presumably to hide his amusement.

“You’re getting very grown, William!” David called brightly, which caused a physical shudder to make its way from the top of Ada’s head to her shins. Then he put one hand on her shoulder.

“Was it terrible?” he asked her, too loudly.

Ada shook her head no. Her voice was still lost.

“Well, how was it? And where’s your briefcase, my dear?” David said.

A giggle from someplace to her right. She looked down at the giant stack of books she was carrying in her arms and back up at her father.

“I lost it,” she said slowly.

He regarded her. In his gaze she saw that he knew what she had done, the intentionality with which she had misplaced the thing, and it shamed her: he would not have cared what anyone said, she thought. And she told herself that perhaps she was not so like him after all — that perhaps she lacked the best parts, the noblest parts, of David.

“How on earth does one lose a briefcase?” David said at last, and then at last he turned and walked toward home, and Ada followed. Her ears burned at the rumble, behind her, of a dozen conversations that resumed, in hushed tones, with more urgency, and the low sounds of laughter that followed.

That night, as she fell asleep, she thought about William, the great beauty of him, the way his sinews fit together in a neat, finished puzzle. And she pondered, for the first time in her life, the particular flaws of David, which she had never before counted, or even noticed: and she wondered what other people said about him, when she was not there to hear them.

From then on, every day, Ada went to school, sat quietly, spoke to no one, waited for her day to end. She longed for the lab, for her work. When no one was watching she coded on the backs of her book covers, until she was caught. At two-fifteen she burst forth from the front door and walked as quickly as she could, without attracting undue attention, to the T, and then took it to the lab to spend her afternoons there, catching up.

Part of her longing to be there was selfish: the work of the lab engaged her in ways that, she thought, her schoolwork never could. But part of it was out of fear, for David’s work was beginning to falter. Now she took copious notes on everything he was tasked with doing. She had always attended meetings alongside him when she felt like it, but now she made a point to, jotting down items as if she were his secretary, his personal assistant.

Quietly, she asked him questions, tried to jog his memory, tried to help him keep up with the demands of his position. “Has Frank written the abstract for the JACM article? You should get it in by next week. Did you call McCarren back?”

At night, after quickly completing the homework that Queen of Angels had assigned, she dutifully told ELIXIR about her day, still eager to feel she was being useful to the lab, still relieved, in some way, to unburden herself to something safe. And, at last, she turned to the work that David had assigned her before his decline. He wrote down assignments for her in marble composition books — the names of pieces of music he wanted her to listen to, the names of proofs he wanted her to solve, books, films, pieces of artwork; even wines that he particularly enjoyed — which, he told her, she could save for later in her life.

As she made her way through them she derived a sense of satisfaction that far exceeded any she got from the homework the nuns assigned her. One day she solved, at last, the Sierpinski proof. She shared this with no one. Next she read a biography of FDR and one of Winston Churchill and one of Albert Einstein and one of Isadora Duncan. Then One Hundred Years of Solitude. Then L’Étranger by Camus, in French. Julian of Norwich’s Revelations of Divine Love.

Slowly, and then quickly, David began to seem less and less interested in his research, which had theretofore sustained and engrossed him completely. It was frustrating to him now: to get to the end of a task and not remember the beginning of it; to forget the names of devices and procedures that he used every day. She whispered them to him when she could. But she was not always there to help. And she could tell now that everybody knew.

His colleagues began to look at him with sad and nervous eyes. Only Liston treated him normally, with a sort of brusque, businesslike vigor that Ada appreciated.

In the winter of Ada’s first year in school, he disappeared twice more, both times for several hours, both times denying that he had been gone, or insisting that he had merely gone for a walk. (Where he had gone on his walks, he could not say.)

They did not go to New York that year for Christmas, nor did they have a Christmas tree. The possibility crossed Ada’s mind that David hadn’t even gotten her a present, until, late on Christmas night, she shyly produced hers for him — it was a rare early edition of The Castle of Otranto, a bizarre favorite of David’s that she had found in an antique shop nearly a year ago and had been saving ever since — and he sprang to his feet. From upstairs he produced a wrapped present for her. When she opened it she saw that it was a sparkly, spangled sweater, and she knew, with certainty, that it was Liston, not David, who had chosen it, bought it, and wrapped it.

By late January she had stopped leaving him alone. Liston, without being asked, began to pick him up in the morning, so that they could travel to the lab together. Ada kept herself awake at night, listening for footsteps descending the stairs, waiting for him to make a noise that would rouse her. She grew weary with fatigue. She grew tired of pretending, to the rest of the lab, that everything was all right.

She hung the front door and the kitchen door with a dozen decorative jingle bells that she’d purchased on sale after Christmas at a nearby store. She rigged up a system that would drop a hammer on a pot when either door was opened, and rested slightly easier. Twice, her makeshift alarm system sounded in the night, and she bolted from her bed and chased after him, down Shawmut Way, guiding him back to his bedroom gently, telling him he was sleepwalking. He was worse at night, or whenever he was tired, less lucid, nearly incapable of intelligent conversation. He called her Mother once. Once, he grabbed her by the wrist and placed her hand on his forehead, as if to tell her he had a fever, wordlessly, plaintively. It frightened Ada. He forgot her name completely on several occasions, and regularly forgot the names of his colleagues. That one, he said, or You know the one. When the DCF agent stopped by, Ada prepped David, subtly, in advance, walking him through the questions Miss O’Brien would ask him by asking him them herself. By the end of their visits he was tired, cantankerous, unlikable. And Ada would do her best to cheerfully distract Miss O’Brien.

Despite all this, he protested that everything was fine.

“I’m perfectly all right, Ada,” he said, in response to any line of questioning about his memory or emotional state. “Really, I’d be much better if everyone would stop haranguing me constantly.”

For months and months, Ada tried to make herself believe that this was true. But at last, in March, shortly after she turned fourteen, Ada walked into his office at the lab. He was staring down at some paperwork on his desk, but he did not seem to be processing it. When she entered he looked up at her, blinking. “Who’s this one, now?” he said.

She knew then that she could not pretend any longer. She walked resolutely down the hall to Liston’s office, and knocked on her door, and felt her face crumple. It was all she could do to keep from crying. She hated crying: it felt to her like a failure of will, a hot and humiliating display of weakness. David did not like it when she cried, and she had never once seen him do it. Miraculously, she held in her tears.

Liston beckoned Ada toward her and pointed to a seat.

“I’m sorry,” Ada said. Her throat was tight. She hiccupped.

“He needs to see another doctor,” said Ada, though she knew, even then, that there was nothing to be done. The disease was rolling in unstoppably, a powerful foreign front, advancing.

Liston convinced David to make her his executor shortly after that, when it became clear that the home visits by social services were going badly. Her childhood friend Tom Meara, who worked for the DCF, had warned her.

Ada, who had become masterful at eavesdropping in the last year, stood in the upstairs hallway of David’s house, the receiver of a telephone extension pressed to her ear, the mouthpiece upended in the air. She breathed as lightly as she could, listening as her father and Liston negotiated her fate.

“They’ll take Ada away from you,” she heard Liston say. “Don’t think they won’t.”

“Really, Liston,” said David, protesting. But in his voice Ada heard something resigned and anxious.

“It would be best for Ada, David,” said Liston. “Right? I mean, wouldn’t it?” And it was then that Ada put the receiver gently down on the table, not wanting to hear anything more. She did not know whom to trust.

Only later did Ada learn all of the details of their arrangement. Mercifully, that year they attempted to keep her protected from whatever backroom dealings in which the two of them were engaging. Even David, never one to shelter her from the affairs of grown-ups, undertook to baby her just a bit, given the circumstances. Or perhaps, more likely, he simply forgot to tell her. But over the course of the following months, it became clear that Liston and David had agreed — whether it was Liston’s idea or David’s, Ada was never certain — that Liston would be designated Ada’s legal guardian in the event that her father became unable to care for her.

On April 1, 1985, David resigned from the Steiner Lab. He did not tell Ada he had done so; she found out only when a grad student let her know that she would really, really miss her father.

“He’s just a great guy,” said the student earnestly. “A classic. There’s not many like him anymore.”

A week later, they received an invitation to a retirement party, formally worded, to be held in a ballroom at the Bit. President McCarren was listed as the host — a fact that made David, even in his somewhat incapacitated state, scoff. Peter McCarren, who had replaced President Pearse several years prior, was despised by David for reasons Ada never fully understood. McCarren was a short, rough man, quite unlike his stately predecessor. He was pushy and red-faced, a bulldog, good at fundraising but bad at math. “That idiot,” David said, anytime his name was raised.

“Good old McCarren,” he said now, ruefully, more slowly than he might have before. “He probably couldn’t wait to see me go.”

The dinner itself was on a Friday night, David’s last official day of work. Ada was to meet him at the lab that afternoon, after her school day ended. In the morning, David had come downstairs in an unironed button-down shirt, and Ada pleaded with him to go back upstairs and put on a suit. She herself ran home briefly after school to change out of her school uniform and into a dress that was slightly too small for her, a pretty one that Liston had helped her pick out the summer before, on one of the shopping trips she sometimes orchestrated for Ada, to David’s mild disgust. The dress, made of light yellow cotton, was too summery for April, and to compensate Ada had paired it with black tights, black patent-leather shoes, and a blue ski parka — her only winter jacket. She had hoped to do without it, but it was still cold that April, and it would not warm up for a month. She looked odd, even she knew it, but she had few other options. She ran to the T through a chilly rain. Inside, she produced the piece of paper she had been carrying in her pocket all day.

This was her secret: at Liston’s urging, she had composed a speech in her father’s honor, a description of his career, the awards he’d won, the impact he’d had on his field. She had stayed up late every night that week, working in her bedroom with one light on, neglecting the homework her teachers at Queen of Angels had assigned her. My father, David Sibelius, it began, is retiring after nearly 30 years of running the Steiner Laboratory. She had crafted it carefully to emphasize his great accomplishments, the nobility of his character, while keeping it relatively restrained and dignified. She had tried to make it funny. If there was one thing David hated, she knew, it was sentimentality.

When she reached the lab she went straight to Liston’s office.

“Don’t you look pretty!” said Liston, standing up from behind her desk, taking off the reading glasses she needed but professed to hate. She, too, had dressed up for David’s dinner: she was wearing an oversized pink blazer that both clashed with and set off her hair, and she had applied more blush than usual. She was wearing big, dangly earrings in geometrical shapes. She would be the one assuming David’s role as head of the lab. She looked as if she had attempted to dress in a way that reflected her promotion, but even Ada knew she had gotten it slightly wrong.

It was 4:00 in the afternoon: three hours before the dinner was set to begin. Shyly, Ada produced from her pocket the speech she had written, and asked if Liston would mind looking at it. Then she sat down on the beanbag chair that she had slept in, often, as a child, and stared at the floor, and waited anxiously for Liston to respond.

“Oh, Ada,” Liston said, “I think it’s perfect.” When she looked up, Ada saw that little pools of tears were hovering precariously above Liston’s lower lashes, threatening to spill over. Liston smiled briefly and then let her face drop. Ada studied her. She was a pretty woman, forty-three that year, slightly plump, soft-featured. To Ada, she looked perpetually like a teenager; Ada had never been privy to the dressing-table rituals and ministrations of women; she mistook Liston’s fashion sense, her dyed red hair, the mascara she wore, for signifiers of youth.

“I’m sorry,” said Liston, and she let out a sad little laugh. “I’ll just miss having you here, that’s all. Both of you.”

All six colleagues filed out, one at a time, from the main room of the Steiner Lab. Charles-Robert, and then Liston, and then Frank, and then Hayato, and then David. Ada left last; and, placing a hand on the wall behind her, she tapped the light switch down instinctively, without having to search for it. She looked backward, into the darkened office, and it felt, in a way, as if she were leaving her life and her body behind: as if, when she closed the door behind her, she would become a ghost, something spectral and disincarnate, something without a home. She wondered if this was what David felt like all the time. She wondered what would happen next.

The dinner was held in the faculty dining room of the Bit, which had been decorated with linens and flowers.

David had already declined to speak, and so he settled uncomfortably down into his chair at the table that had been reserved for the six of them, along with the provost, President McCarren, and Mrs. McCarren, a tidy woman who tried to make polite small talk with David until, at last, she gave up hope.

David’s posture was slumped; his head hung low; when people spoke to him he did not meet their gaze, but turned his own to hover someplace around their mouths, as if trying to read their lips. He did not eat until he was reminded to by Ada. He smiled politely as, one after another, his colleagues at the Bit, and some from other institutions, spoke about his achievements and intelligence, his wit and generosity; but the naming of these qualities was, to Ada, only a cruel reminder of their recent disappearance. David got tired easily now. Once or twice his eyes closed completely, and Ada jostled him as subtly as she could.

Ada was due to speak last. She felt in the pocket of her coat, which she had insisted on hanging over the back of her chair, for her speech. The paper, by then, was soft with the wear of being handled, being worried over. She produced it and put it in her lap, glanced down at it when she could. But as dessert was being served, and while the provost was speaking, David turned to her and asked, too loudly, if she was ready to leave.

Ada shook her head once, quickly. President McCarren had heard him. Ada was not certain how much the rest of the university knew about the reasons for his retirement — certainly the other members of the lab were protective enough of David not to have said too much to anyone — but in that moment she realized that everyone must have known that something was wrong with her father.

“Come now, Ada,” said David. “Really, let’s go.”

Politely, McCarren averted his gaze.

Ada leaned toward him and whispered to him urgently. “It’s for you,” she said. “The dinner is for you. We can’t leave yet.”

David was shaking his head slowly, as if he had not heard her. “I’ve got to go,” he said, and unsteadily he stood up from his chair. He held a hand up to the rest of the table. “Okay,” he said, “bye to all, now.”

Ada stood up, too. She wanted to reach out to him, to pull him forcibly back by his elbow, but she felt that that would be worse. Her speech fell from her lap onto the floor and she bent to retrieve it. Without meaning to, she caught Liston’s eye as she rose, and on her face Ada saw a look of such sadness, such pity, that she quickly turned away. Together, she and David left through a side door. And behind her, Ada heard the provost stutter and then pause.

“Well,” he said, “I guess our guest of honor is indisposed. .”

Then they were outside, and they stood together for a while on the sidewalk while Ada decided what to do next. The rain had stopped but it was bitterly cold, too cold for April.

“Can we take a cab?” Ada asked — something that David abhorred. To him, taxis were for the lazy, the fiscally irresponsible. But she thought it was worth asking, for she was shivering even in her ski parka, and that night he immediately agreed.

In the taxi, Ada was silent, furious. She said nothing except to give the driver directions, when David failed to. David rested his head against the headrest, closing his eyes for a while. She looked over at him resentfully. In the yellow light from storefronts and streetlamps, he looked sickly and old. She had been noticing lately that his physical size was shrinking: although he had always been thin, he had seemed shorter, recently, more stooped: as if he had aged five years in a week. His eyes had dark circles beneath them. She supposed he had been handsome once; his stature had helped him to be so. He was uncommonly old when she’d been born, yes, but he’d always seemed young for his years. He was tall and well built, at least, with fine features and bright, inquisitive eyes. When he felt like it, he was capable of listening intently for hours on end. Women had always liked him: Ada was not oblivious to this fact. But he was changed now. More like a grandfather than a father. Someone incapable of offering her protection. She felt unsteady and unsafe.

At home, Ada retreated to her room without saying good night. She turned on her computer, pulled ELIXIR up to have a talk. And then she heard the sound of David’s footsteps on the stairs, heard a faint knock on her door.

It was rare for David to come into her room: she had no memories of him sitting on the edge of her bed, reading her a story as she drifted to sleep. Though he read to her, it was always downstairs, in the living room, in a somewhat businesslike manner: she sitting in one chair, he in another; and when she tired, Ada would trot upstairs and put herself to bed. At four years old she knew how to brush her teeth, wash her face, comb her hair so it would not tangle; she knew how to don her nightgown, to tuck her little body into bed.

Now she went to her bedroom door and opened it a crack. She was still wearing her ridiculous outfit, banana-colored dress, heavy black tights.

David looked distressed. The light in the hallway was off. She could see him only in the light cast upon him by her little desk lamp.

“May I come in, Ada?” he said.

She opened the door a bit more. There was only one chair in her room, at her desk; David claimed this, so she sat down on her twin bed, across from him. He looked at her seriously.

“I want to apologize,” he said.

Ada was silent.

“I’ve spent a great deal of time denying what’s become undeniable recently,” he continued. “That my mind is most certainly being taken from me, slowly. This is a truth that I have found it difficult to confront.”

She looked at him. She felt recalcitrant, unswayed.

“I can tell you’re upset. While I have my wits about me,” said David, “while I am relatively mentally intact, I want to tell you what it has meant to me to have you as my daughter, Ada. You cannot imagine.

“Now—” he said, holding up one hand to stop her as she opened her mouth to speak, “Now. It is true that great innovations in the field of medical research and technology are becoming. .” He trailed off, looking down at his palms, as if wishing for notes.

“Innovations in medicine and technology,” said Ada.

“Yes,” said David. “There is a chance that some intervention will occur in my lifetime that will reverse the course of what I now see as my inevitable decline. A small and improbable chance, but a chance nonetheless. That said, I don’t think you should cling to this hope. Because, as we both must accept, the likeliest course of events is that I will die before you’ve reached adulthood. And therefore that is my prediction, and that is the path for which you should prepare yourself.”

Ada nodded. She was sitting very still on her bed. She was still wearing her coat. Her right hand was in her pocket, grasping the speech she had written about her father. She wondered whether she should give it to him.

“It is also possible,” said David, “that you will one day learn some things about me that are difficult to understand. I think every child goes through this process. The problem is that I will not be here — perhaps mentally, perhaps physically — to explain them to you, or to guide you through them. And therefore you must trust me when I say that everything I have done has been out of a wish for a better life for myself and for you. And everything I have done has been in our best interest. All right, Ada?”

She didn’t move. She watched him. His gaze was beseeching. He leaned forward in his chair to look at her.

“Do you understand?” he asked her. And, at last, she nodded, though at that time she did not.

“Finally, I have never been a religious man,” said David, “but I also have some notion that this is not the conclusion of our story, my dear. I think it quite possible that our paths may cross again someday, whatever that may look like.

“Thank you for listening,” said David. He stood up, somewhat painfully, and walked to the door. “I’ll miss talking with you most,” he said. And then he was gone.

They never spoke this way again. After much consideration, Ada did not give him the speech she had prepared for him, thinking that he would deem it too maudlin. Instead, she kept it for herself, reading it occasionally to remind herself, as her father declined, of how he used to be.

The morning after David’s retirement was an odd one. It was a Saturday, and there was no reason to leave the house. No lab to go to, even if they had wanted to. David was quite still, and sat with a book of poetry near the windows at the front of the house, not really reading. “At last, some free time,” he said, feigning cheer. “I’ve been meaning to get to this for years.”

Ada made a lunch for both of them of pickled herring sandwiches on white bread, his favorite, and cut them into dainty crustless bites, and served them with strong tea. Afterward she begged him to walk to the library with her, simply for something to do, and he agreed.

He looked at the librarian, Anna Holmes, without much recognition, even though she had worked there for years and called him by name, and even though Ada had once wondered, idly, whether the two of them might have crushes on one another.

“How are you, David?” asked Miss Holmes, clearly happy to see him. “It’s been so long!”

David looked at her quizzically. “Quite well,” he said. “Thank you for asking.”

Later, Ada read and worked on problems until it was time for dinner and bed, where she prayed without much faith or conviction for the healing of her father, thinking of Julian of Norwich, of Franny Glass.

Sunday was much the same.

And then, on Monday, it was time to go back to school. Ada admonished her father not to leave the house. Their exterior doors, original to the house, could be locked with an old-fashioned skeleton key from the outside. Ada hesitated, but then decided, feeling guilty, that it would be best and safest for David if she did so that day, and every day thereafter. She had not told anyone about David’s recent wanderings: she feared they would take him away. After her school day ended, she raced home, hoping desperately that he had neither broken out nor panicked, that she would not find him reduced to tears on the floor, or find him in some other, equally upsetting position. But he seemed fine, sitting placidly in his chair by the window, gazing out of it.

In the ensuing weeks, Ada attempted to extract all the information she could before it faded. But he grew more and more reticent.

“I simply can’t remember, my dear,” he said tiredly.

So instead she wrote down memories that he had at one time or another shared with her, to the best of her memory: that her grandfather was the grandson of Finnish immigrants who made their money, upon arriving in the United States, in shipping; that her grandmother was a descendant of William Bradford, the British Separatist, the Mayflower passenger, the governor of Plymouth Colony. That his mother’s maiden name was Amory. All of this Ada wrote down in a blue-covered notebook, separate from the marbled ones in which David wrote his assignments.

When she asked him to confirm what she had written, reading the facts aloud, he told her that he could not recall. “Amory?” he said to her. “I’ve never heard of it.”

Ada called this period in David’s life “working from home,” to preserve her sense of hope and his sense of dignity, and each day she set out some task for him to complete, and on weekends she brought home several newspapers and pored over them with him.

He became increasingly obsessive about ELIXIR. Interacting with it seemed to be the only thing that brought him solace anymore. Sometimes, when he had trouble finding the words, he simply pointed to the office; and then she walked him into it, and sat him down at his computer. She opened ELIXIR for him, and left the room, out of respect, and let him type.

“Now you,” he told her, when he had finished, and it occurred to her that perhaps he had the conviction that ELIXIR was his legacy. She signed him out, signed herself in. Dutifully, she conversed with the machine.

Sometimes she still tried to encourage him to focus on his work. But mainly he just sat in front of it, looking at it silently for long stretches of time — a puzzled, painful look on his face.

Sometimes she brought out the floppy disk he had given her one August night two years prior, at the end of his failed dinner party. For Ada was still marked upon its hard cover, in David’s handwriting; a note from him to Ada was still affixed to the disk itself. She inserted it into the disk drive. Then she sat down with David in front of it, and asked him to help her solve it. DHARSNELXRHQHLTWJFOLKTWDURSZJZCMILWFTALVUHVZRDLDEYIXQ, read the text file. It looked completely arbitrary. David was quiet at these times, watching as she wrote down, on pieces of paper in front of her, the letters that appeared before her on the screen. As she tallied their frequency, made slash marks above them on the page.

One day, Ada turned the computer on and it displayed an icon of a frowning, X-eyed monitor, and would not boot up at all.

David pointed at the computer screen. “Just like me,” he said, about the sad little Mac on the screen, and Ada laughed in relief that he could still make a joke.

She vowed to fix the computer, but she couldn’t.

“Time for ELIXIR?” David asked daily — he had retained the word surprisingly well — and she had to tell him that his Mac was broken, and bring him upstairs to use hers instead.

While he worked, she tried and tried, in his office, to fix whatever was preventing his computer from starting. In light of David’s illness, the state of the machine took on greater meaning. But she couldn’t. She needed David’s help, and he could no longer give it.

At the time of David’s retirement, the lab was working on a system to increase ELIXIR’s vocabulary by training outsiders to chat with it correctly, which David had always been opposed to. Liston, the new director, discussed the lab’s progress with Ada in bits and pieces each time she saw her. Prior to the onset of David’s disease, she had always seemed hesitant to involve Ada in the work of the lab — not because she doubted her ability to learn it, but because long ago she had unofficially designated herself a counterbalance to David in regard to Ada’s well-being, and as such pushed her gently backward into childhood to the best of her ability while he beckoned her forth. Now that David was fading, however, Liston seemed to realize how much Ada missed the work, and included her in it whenever she could.

She came over for dinner once a week, sometimes bringing Matty, her youngest, when she could convince him to come along. He read comic books in a corner, looking at all of them suspiciously from time to time, not saying much. Other times she came alone. And she updated Ada on the work of the lab, the problems they’d encountered, the tangles they were working out. Ada sometimes tried to help remotely, presenting her findings to Liston the next time she saw her or spoke to her, once calling the lab with a solution that had presented itself to her suddenly in the middle of the previous sleepless night. “Thank you so much, honey,” said Liston, and Ada heard in her voice that they had fixed it themselves already.

At school, Ada was distracted. She had settled into a painful, uncomfortable existence at Queen of Angels: she rarely spoke, except when directly called upon. Not wanting to ask David to buy her a backpack, and properly humiliated out of ever using a briefcase again, she settled on simply carrying her books in her arms everyplace she went, which earned her odd glances and several nicknames that she overheard despite her best efforts to tune out every conversation around her. She had no friends, nor had she any enemies, really. She brought a novel to lunch each day, balanced at the top of the stack of her schoolbooks, and read it while she ate slowly, neatly, making certain with searching hands that she had wiped her mouth clean after every bite.

Simultaneously, she felt invisible and too observed, and she fantasized at times about what it would be like to be amorphous, incorporeal — the manifestation of the vision she had had upon leaving the Steiner Lab for the final time — a shadow-girl who could slip imperceptibly around corners and through hallways, keeping close to the wall. She existed but was not seen. In the privacy of her room, under cover of night, she sometimes practiced the mannerisms and dialect that she had seen children her own age using. Like, she whispered to herself. Um, totally. Whatever.

She longed, now, to be pretty. After weighing the evidence, she had recently decided that she was not, which, in her former life, would not have mattered — in fact, David had always seemed to consider prettiness a detriment, something hampering and debilitating, like a tin can tied to one’s leg.

But at Queen of Angels, prettiness was all. Melanie McCarthy was the standard-bearer in this realm, and everyone else in the eighth grade could be ranked in descending order after her. Ada was, she felt sure, near the bottom. In the mirror, she took off her glasses, and her reflection became hazier, softer. Better. She put them back on and frowned. The glasses themselves, she thought, were maybe the problem; but to ask David for contacts would be unthinkable, akin to asking him for something like breast implants. She went to bed, sighing long sighs, dreading the morning.

As David’s mental decline accelerated, Ada clung to his physical presence in the house, and dreaded the day when he would not be there. She reverted to an old pattern: when Liston came over for dinner now, she worked her hardest to convince her that he was well, that his mind was sharper than it was, his memory more capable. She coached him on topics of conversation in advance, went over the day’s headlines with him, as she used to do herself before the dinner parties he once threw. “David was just saying,” she would begin, and then dispense an opinion that she herself had constructed after a careful perusal of world events. “Right, David?” she asked him, and he would look at Ada vaguely and nod. He had always been kind to Matty and he continued to be so. When it occurred to him, he gave Matty some little token each time he came over, a book or a fancy pen or a piece of chocolate. Sometimes the chocolate was too old, and Ada had to swap it out for something else, but mostly Matty didn’t notice. With time, though, David forgot Matty’s name, and then forgot him altogether. “Who’s this young fellow?” he began to ask, and Matty seemed terrified of him, avoiding his gaze, finally refusing to come altogether — Liston didn’t tell Ada this, but she knew it to be true. Liston protected her. “He’s got baseball practice in the evening now,” she told Ada. “William takes him over.”

The rest of the members of the lab stopped by from time to time at first, but soon their visits dwindled in frequency, and now when David forgot their names it made Ada perversely satisfied. If they came more, she thought, he’d know them better. Still, she prompted him, wanting them to think well of him and of her, too, cheerily glossing over the extent of his deterioration. When Regina O’Brien came for her monthly visit she employed the same techniques. At the end of each visit she took Ada into another room and asked if she felt comfortable living in the home and she always, always said yes.

For a time it seemed to be working. Ada felt she could take care of her father. Sometimes, when he fell asleep at his desk or in his chair, a book in his hand, unread, Ada sat across from him and imagined him back to his previous state — imagined that when he woke he would spring up vigorously from his chair, and beckon her into the dining room, and lay out before her some famous proof or problem, and set her to work upon it, spinning her like a top. “Very good, Ada,” he used to tell her when she solved it. “Excellent work. Smart girl,” he would say — benedictions that she craved, now, beyond all measure. Well done, she whispered to herself at times, when she solved a problem that she’d assigned herself, from the notebooks David, in his former incarnation, had created for her. Well done, you clever girl. And she imagined that David was saying it.

She got by in this way. She managed. She vowed to keep up the charade of David’s competence for as long as she could. And then, in May, David walked out of his room without his clothes on, which mortified Ada to the point of incapacitation. “Get dressed!” she said abruptly, and then she ran and hid in her bedroom. When she emerged he had, thankfully, complied. But he did this with some frequency thereafter, until she began to lay out his clothes for day and night upon his bed, ordering him to get into them when it was time, and closing his bedroom door behind her while he did so. “Are you dressed?” she asked him, and only when he replied affirmatively did Ada enter.

Often he grew frustrated as he searched for words. “The thing that’s like a wrench, but not a wrench,” he said. “The thing that’s black and small. The thing that you use. The thing that I love.” And then, when thing eluded him: “I want it. Where is it?” There were times where she could not help. Next, he began to swear at her — she had steeled herself for this, having read several scholarly articles that indicated that the aphasia associated with Alzheimer’s often left one’s arsenal of curses, located in a different region of the brain, unaffected. But the reality of it shocked her: gentle David, calling her words that he had never before even used in her presence. David, who deplored cursing. He knew her less and less, sometimes raising a fist at her as if in anger and then letting it drop to his side; sometimes weeping like a small child, which troubled her soul. “My friend,” he said, by then, about all people, in order to avoid their names. Including his own daughter. “Ada,” she sometimes said in response. In front of Liston, she pretended it did not bother her, but in private she railed at him from time to time. “You know my name,” she said to him testily. And once or twice she had yelled at him with her full voice. “I’m ADA,” she had said. “You named me Ada.” She had never before shouted at him, and it felt terrible and thrilling all at once. In those moments he blinked at her; he did not flinch. He seemed aware, somehow, of the importance of keeping his pride intact, a citadel, as his mental faculties crumbled around it. And as Ada wailed at him, shouting her own name, he would turn his head slowly to some nearby object and gaze upon it. Other times she whispered it to him, her name, imagining somehow that it might seep into his consciousness subliminally. While he was sleeping. While he was awake, and staring blankly out a window onto Shawmut Way. I’m your daughter Ada. He did not respond.

More and more, every week, he tried to wander. The bells went off in the middle of the night. She leapt from her bed. She grew weary.

One day, Ada came home from school to find three large fire trucks lined up along Shawmut Way. Liston, in her work clothes, stood outside of David’s house, speaking to a firefighter; their neighbors stood nearby in little groups. Even Mrs. O’Keeffe had gotten up out of her lawn chair for the occasion, was leaning on her cane, straining to overhear what they were saying.

It was then that Ada saw David, sitting on the ground, a blanket wrapped around him despite the warm weather. A firefighter was sitting next to him casually, attempting to chat with him as he sat there on the grass. He looked childlike and confused, a five-year-old waiting for his mother. His feet were pointed upward toward the sky. His head hung low, and he was shaking it almost imperceptibly from side to side. In the spring air Ada picked up the smell of something acrid. Smoke, she realized. Her instinct in that moment was to run. But then Liston turned and saw her and strode toward her quickly.

“Ada,” she said, “honey. Did you lock him inside? Was David locked inside every day?”

Ada felt something rising up inside her: it was the unfairness of it all, of being expected to watch over David, who was supposed to be watching over her. She felt simultaneously ashamed and self-righteous. What else was I supposed to do? she wanted to ask Liston. Her father was her responsibility, not anybody else’s — and she had made the best decision she could make.

But she could not articulate any of this, for her voice had been taken from her. Instead she stood in place, looking down, her arms folded tightly about her waist, waiting for someone, anyone, to recognize the injustice of it all. Until, at last, Liston put an arm around her and led her down the street.

St. Andrew’s Manor was in Quincy, just outside the city. It was a nice place overseen by an order of nice nuns. Liston’s own mother had ended her days there after a debilitating stroke. Shortly after the day that David almost set the house on fire — as it turned out, a neighbor had heard the sound of the smoke detector going off for too long and had called the fire department — Liston had had a serious conversation with Ada. And, at last, Ada gave her consent: David would no longer live with Ada on Shawmut Way. Liston, as previously agreed, would assume full guardianship of Ada — who, at fourteen, was four years from legal adulthood. And David would move into St. Andrew’s.

When Ada first heard the name of the place, she thought it might be something fancy: a country house with a semicircular driveway and a stable, a Tudor mansion set back in the woods. Liston said that all David would need were some clothes, maybe some pictures to put on his shelves — at which point Ada realized that they had no pictures, nothing they kept in frames around the house. Liston’s house, on the other hand, was decorated almost exclusively with photographs of her sons and daughter and her grandson; or friends of hers, with Liston, at the beach; or family. She even had pictures of Ada in the lab, on Halloween, at their Christmas parties. Shyly, Ada asked her if she might take one of these to bring along with David so that he would be able to remember her. They had almost no pictures in their home; David’s camera-shyness meant there were none of him, and he rarely thought to take a picture of Ada.

“Of course, baby!” said Liston. “I think that’s a really good idea.” And she brought Ada over to her house, and let her choose any one that she wanted. After some consideration, Ada selected one from a photo album, perhaps three years old. In it, Ada was sitting at the monitor in the main room of the lab, chatting with ELIXIR, smiling happily toward the camera, but looking up above it; for, she remembered, it was David she’d been looking at. David, who had been standing behind Liston as she took the shot, saying something silly about formaggio or fromage.

Liston selected a few more and said she would find frames for them all. And then she put a hand on Ada’s shoulder.

“It’ll be okay, kiddo,” she said. Ada looked up at her warm face and wanted badly to smile for her, but she found that she couldn’t.

The morning of David’s departure, he seemed more confused than usual. He hardly spoke. Ada and Liston had spent the previous evening packing his clothes into a large suitcase, and, beholding it, David put one hand to his cheek plaintively.

“But where are we going,” he said, over and over again.

“We’re moving!” said Liston. “Someplace great. An adventure.”

“No, thank you,” he said politely, at one point.

Just before David walked out the kitchen door for the last time, Ada had the urge, suddenly, to tell him to look around the house once more. To go down into the basement, to place a hand on his work desk; to go up into the hot and dusty attic; to go and sit on his old bed for a while. Did he know that this would be his last glimpse of the house he had grown to love?

But Liston was guiding him out the door already, perhaps to avoid upsetting him.

“Where are we going, now?” asked David, one last time.

“Put your seat belt on, honey,” Liston said to David.

He complied, and then let his arms fall limply at his sides. From her place in the backseat, Ada gazed at his hands. In the left one he was clutching his lucky charm, the clover-shaped trinket he usually carried with him. Recently it had comforted her to see him holding it — at least, she’d been telling herself, he remembered to put that in his pocket each day — but that day it pained Ada to see it, bespeaking, as it did, some unfulfilled wish. His hands, around it, looked doughy, inflated somehow, too large for his body. They didn’t look like the hands of a working man: nothing like David’s strong hands as they flew about at one time, dismantling things, reconstructing them, chopping and stirring his meals. Recently, she thought: less than two years ago.

“What sort of place is it,” David was saying. “And tell me the name again.”

“St. Andrew’s Manor,” said Ada, hoping that the sound of the name would please him—manor being a word that, she imagined, might have similar connotations for him as it did for her. Of dignity, of prestige, of gray impressive stone.

But what he said was, “Oh, of all the things,” and she wondered if this was a specific response to the name, or simply an arbitrary outburst, evidence of the way his temper had been flaring recently at odd, unpredictable moments.

Phrases like that one had become a catch-all for him, when he couldn’t muster a more appropriate response. For heaven’s sake. Good heavens. I’ll be damned. It reminded her of the way ELIXIR had been given a set of responses to use when nothing else was available. David reverted to them frequently by then, and when he uttered them she read in his eyes a certain disappointment that he could not conjure up a more precise choice of words, volley quickly back the best response. Finding the mot juste had been a skill on which he had prided himself for as long as Ada could remember. Before the illness, he had loathed puns and loved cleverness in equal measure. Words, to David, were nearly mathematical: there was very clearly a correct one for every slot in every sentence. When he was at his sharpest he rolled them into place like a putter on a green. Now a good day meant that he could come up with a dozen in a row that were appropriate to the situation at hand.

In the front seat, Liston was making small talk. She feigned cheerfulness for David’s sake, to keep him settled, but she glanced at Ada in the rearview mirror every few moments. And Ada looked out the window. Liston had told her, again and again, that this was the best thing for David, that he couldn’t be cared for safely at home, not anymore; but since the decision had been made for him to go to St. Andrew’s, Ada had been envisioning, almost obsessively, other lives, other plans, for herself and her father.

She daydreamed often about running away with him, to New York City, to a different country, to the cabin in the woods of the Adirondacks that David had rented for years. (Conveniently, these daydreams simultaneously allowed her to envision leaving behind her education at Queen of Angels, as well.) And when she was not daydreaming, she was paying extra attention to David’s mannerisms, his appearance, his gait. She wanted to memorize them. With the little camera she rarely used, she had recently been taking photographs of him, surreptitiously, in different places in the house. Later, these would look to her like pictures of a ghost. In them, he was expressionless. Gone were David’s funny, theatrical, changing features; in their place was the lion face she had read about in articles, a term that frightened her with its implication of cruelty, its implication that the bearer of such a countenance might suddenly eat her alive. Instead she tried to think of David’s face as a doll’s face. A still and quiet mask.

Liston turned right at a sign that bore the name of the facility in an even font that reminded her of the lettering on banks: ST. ANDREW’S MANOR: EST. 1951. At the top of a small hill sat several low brick buildings in the shape of a U. Liston pulled her car into the parking lot, and Ada saw the fingers of David’s left hand curl into a fist. She leaned forward to take in the view. Two old women, much older than David, sat in wheelchairs on the paved driveway that abutted the front entrance. They were slumped in their chairs. One seemed asleep, her head lolling forward on her chest. The other moved her feet back and forth slowly, as if trying to get up and walk.

The three of them got out of the car, David only after Liston’s prompting. He was relatively able-bodied, still, and he got up quickly from his seat and closed the door behind him in one easy motion.

There was a plaque to the right of the white front door that identified Andrew as the patron saint of fishermen, and once Ada got inside she saw why the place was named for him: the large rear windows of the lobby looked east to the harbor some distance away, visible from the building only by virtue of the elevation of its plot of land. Still, Ada could see boats there, sailing inland and out, and it was a sunny day, which made everything seem a little less dismal. The rest of the lobby was drab and beige, with floral patterns on the pillows, with arrangements of armchairs and tables and books she was certain no one ever looked at, and two fireplaces that looked similarly untouched. They might not even work, she thought, and she wished that they did: David’s love of fireplaces was well known to everyone who knew him.

David stood and looked at the ocean while Liston navigated the front desk. Ada was grateful to her for doing this so that she didn’t have to. She had a speech prepared to make to the administration and staff about David’s needs and concerns, but it had gone out of her head, and she stood with David and stared. In a moment of self-awareness, she closed her jaw. He seemed too young to be in this place, she thought. Who would he talk to? She vowed to visit him every day, taking two buses from Dorchester to Quincy.

After a moment two administrators emerged from a hallway, one a Carmelite nun.

“How are you, Sister?” said Liston cheerily. It was clear from the nun’s response that she remembered Liston from her mother’s time in residence. As she introduced herself, Ada was uncertain about whether to shake her hand. She had not shaken the hands of any of the nuns who taught her, upon meeting them. But this one offered hers to Ada kindly, and she took it very gently, ignoring the admonitions David had always given her about being firm and businesslike when she gripped anybody’s hand in greeting. She was younger than Ada had thought most nuns to be — she must have been very young indeed the last time Liston had seen her — and she said her name was Sister Katherine. The other administrator was Patrick Rowan, a middle-aged man with stale breath and a wide blue tie. Ada immediately disliked him for the way he took David’s hand with one of his and put an arm behind David’s back. As if David were incapable of walking. As if he needed anyone else to navigate him in this way. David, too, recoiled.

“Oh, for heaven’s sake,” said David. “What a production.” And Ada felt warm with satisfaction that he had produced such an appropriate response.

Their little group walked down the hallway toward a wing called the Mount Carmel Center for Memory Care, and stopped outside a set of double doors. Patrick Rowan punched in a code and the doors swung open. As Ada walked through them she turned back over her shoulder and noticed an identical keypad on the opposite side. Clearly, there was no leaving this wing without the password.

After several turns that left her feeling disoriented, she came to David’s room. On the wall outside it was a placard with two paper cards slid into it: one that said Mr. David Sibelius — Doctor, Ada thought to herself, not Mister—and one that said Mr. John Gainer. Inside, she saw that David’s roommate was ancient: to her he looked a hundred or more, though later, as an adult, she realized he had probably been closer to eighty-five. He said nothing to them as they entered. He was a small man, sitting in a recliner that cradled him like a hammock, his back bowed, his little neat feet sticking up at the end, an enormous magnifying glass in one hand, looking through it at a book that he did not lower as their party of five entered the room.

“Good afternoon, Mr. Gainer,” said Patrick Rowan loudly. And then he turned to Ada and said, in a normal voice, “Mr. Gainer can’t hear much.”

He brought David toward Mr. Gainer and bent down, placing a hand on his shoulder.

“This is David Sibelius,” said Patrick Rowan. “Your new roommate.”

“How d’you do?” said Mr. Gainer, and David nodded formally.

The room was large and decorated sparsely. A brown wooden crucifix, like the ones at Queen of Angels, hung above the door on the inside wall. Ada wondered if it was David’s roommate’s, or a standard part of the décor in every room. The two twin beds were on opposite walls, and on Mr. Gainer’s bed there was a blue crocheted blanket that somebody — his wife? Ada wondered — had made for him. There were two matching recliners that looked quite comfortable, and two wooden-backed chairs. Two dressers. Two nightstands. Two bookshelves mounted to the walls above the beds, too small for the collection of books still sitting in Liston’s car. Not that David read much anymore — but Ada had imagined that to have his favorites with him would be comforting, like the photographs of her and their friends that Liston had brought along. Disappointingly, the large window opposite the door looked out at the parking lot. She wished he had had a harbor view. The ceiling was made of large panels that looked to her like Styrofoam; she had the impression that they could be taken out quite easily from movies she’d seen involving heists. (Briefly, her mind wandered once more to absconding with David.) The floor was blue vinyl. The overheads were painfully fluorescent: a type of light that David despised and found depressing. He had commented on it all his life, whenever they found themselves in restaurants or stores where they were employed. “If only they’d do something about the lights, though,” he had lamented, in certain locations, in the past. He had even coaxed Tran into using incandescent lightbulbs several years ago, offering to pay for them himself. Now he was looking around his new room. He circled it once, slowly. He opened up a small drawer in the nightstand. Into it he put his lucky-clover charm. He closed the drawer again. He offered up a closed smile. “I’ll be darned,” he said, as Sister Katherine moved about the room, smoothing the tightly made white bed, fluffing the pillows.

“Now, Ada,” she said, “I’m going to write down David’s direct line for you, all right? This is his phone number,” she said. “You can reach him anytime. And David, you can call Ada anytime, too. We can help you.”

She took a small pad of paper out of the breast pocket of her large dark blazer, and, after writing on it, ripped off a piece of it and handed it to Ada. David smiled faintly.

“Our residents are very happy here,” she said. Ada believed that she believed this. “Isn’t that right, Mr. Gainer?” she asked, raising her voice, but Mr. Gainer had already gone back to his book, and he did not know he was being addressed.

“I know Mom was,” said Liston politely.

Liston sat with David on the edge of his bed while Ada ran back and forth to the car, unloading his possessions with the help of a metal dolly that Patrick Rowan found for her.

When she had everything set up, she asked him if he’d like anything moved. Slowly, he looked about the room. He walked to the bedside table and touched one of the photographs that Liston had framed: it was a shot of the group of them, the Steiner Lab, leaning forward over a dinner table at a restaurant that Ada could no longer remember the name of. It had been taken perhaps four years prior — Ada looked noticeably younger and smaller in it, and Liston’s hair was a slightly different shade of red. David, as usual, was missing from the shot; he’d been the photographer. The restaurant, a Thai place they had gone to only once or twice, had since closed. Ada had liked it: they all ate shoeless, sitting on the floor, their feet in a little sunken pit below the table, and her chicken and cashews had come served in half of a hollowed-out pineapple. “They probably reuse that time after time,” Liston had said, horrified, but Ada and David had not cared.

This was the picture David lifted, now, from the table. “Amarind,” he said suddenly. The name of the restaurant. And Ada wondered if they had made a mistake, admitting him here.

They stayed with him through lunch, and Liston tried to make friends on his behalf. She charmed the staff, one of whom, a woman named Peggy, had grown up next door to her in Dorchester. Some of the others she knew as well—“Oh, she’s terrible,” she whispered to Ada, upon seeing a tall, thin, spectral woman at the end of a hallway, and she turned them all abruptly in the opposite direction. She waved to the other residents, asked them their names, introduced David to them as they all walked by. Ada did not want to admit it to anyone, not even herself, but she was frightened, being there. The old people around her frightened her. Some of them were slumped in their wheelchairs, tilted, askew. Later in her life she would seek out the presence of older people, find them comforting, find peace near them; but now she avoided their gaze. It could not be comfortable, she thought, for some of them to be alive. One of them approached her too quickly, called her by the wrong name. “There she is,” said the old lady, “Oh, Patty, I didn’t know where you’d gone.” Ada walked by her, facing forward, and said nothing. She realized that David had said such things, was capable of saying such things. But he was familiar to her, at least. She had watched his slow progression. In him she could still see some essential David-ness, and still, in most ways, take comfort in it.

After lunch, they walked him back to the common area adjacent to the dining room, where Mr. Gainer was seated at a card table, staring at a puzzle that had already been completed.

“Why don’t we sit here for a while?” said Liston, and she perched on the arm of a floral sofa while Ada and David sat in it, and made cheery conversation with the two of them, and with everyone else in the room.

“This was my mother’s favorite place to sit in the evenings, before dinner,” said Liston, and just for a moment, through Ada’s own sadness, she recognized the sadness of Liston, the pain that she must have felt at the loss of her mother. It was something she had never truly considered, about adults. She had always somehow imagined that the loss of a loved one would hurt less for them: that it would feel like something natural; that they would be calm and practiced and dulled to death. In fact, she was counting on it: for she had been telling herself that if only David would hold on to life for the next decade, by the time she was twenty-four she would be better equipped to handle his absence. But something in Liston’s voice, as she spoke of her mother, made Ada realize that she had been incorrect in this assumption.

Twenty or thirty minutes passed by and then Liston looked at her watch. They had been there for nearly six hours, and Ada knew that she would want to get home for Matty.

“It’s time for us to go, David,” said Ada, so that Liston would not have to.

He nodded slowly.

They walked him back to his room, and then he sat down stiffly on his bed, his hands on his knees. He looked too thin. He did not look at her. A flash of anger overcame her suddenly: at the unfairness of it all. He was not like the rest of them, she thought — he could not possibly belong here, in this place, full of the dying, the near-dead. Snap out of it, she wanted to tell him. Wake up.

“I’ll see you tomorrow,” said Ada instead. And as she left him, walking slowly down the hallway, she willed herself not to look back. She thought of the story of Lot’s wife, and of David’s voice as he had told it to her, many years ago.

In honor of Ada’s first evening as a member of the Liston household, the head of it had planned a family dinner. She had commanded her boys to be there, and invited her daughter Joanie, too.

“I’ll be right back,” said Ada, when they pulled onto Shawmut Way. And then she returned briefly to David’s house to gather together a few more things before moving, permanently, to Liston’s. Just as she had done a year ago, the first time David disappeared, Ada packed some clothes and books into a little suitcase, and then for a moment she paused and sat down briefly on her bed. She looked around the hot, close room that had been hers since she could remember. It was an eaved chamber with a half-high closet, in which hung the few items of clothing she presently owned — each one of which David had bought for her, whenever he had thought of it, or whenever he had been reminded to by Liston — and some from the past that she was particularly fond of. The dirndl he had purchased for her in Munich, which she had long since outgrown. A little pair of Dutch wooden shoes, hand-painted with tulips. A beautiful silk kimono, purchased in Kyoto. She went through all of these now, tenderly, remembering each trip, forcing herself to consider the idea that she would not ever take a trip with David again. Then she folded the several shirts she had that currently fit her, and her one pair of jeans, and underwear and socks, and the several training bras that Liston had taken her to buy two years ago, stealing her away from the lab for the afternoon.

“Tell your father if you want to,” Liston had said. “He won’t care.” And he wouldn’t have, but Ada didn’t, telling herself — out of embarrassment — that it was not necessary. They didn’t fit her properly anymore; she would have to work up her courage either to tell Liston or to venture into a department store by herself.

All of these items she packed into her little blue suitcase. Its faded leather had reminded her, always, of the skin of an elephant: an observation that had once made David laugh aloud.

Then, at last, Ada walked down the wide wooden staircase that took her to the first floor, bearing her suitcase bravely in her left hand, and hanging on to the banister with her right. How many times had she walked down this staircase in anticipation of some new discovery, some new lesson that would be imparted to her by her father, her creator? Some conversation that would open before her a new dimension of the universe, a new chapter of the history of the world?

Ada was relieved to find, upon entering Liston’s house, that her sons were nowhere to be found. Dinner was planned for 6:30.

“Everyone’s out,” said Liston, “but they’ll be back soon. They’d better be, anyway.”

Then she showed her up to her new room, Matty’s old one, which, in the last week, Liston had stripped of its boyishness and made as plain as she could. Matty had now been given permanent residency in Gregory’s room — Ada shuddered to think how Gregory might have reacted to this change — and the race-car bed had been moved with him. A twin bed with a dust ruffle and a pink-and-orange afghan — Joanie’s when she was small, said Liston — had replaced it. A small pupil’s desk with a lid that opened upward was pushed against a windowed wall, and a pine dresser, emptied, had been positioned near the closet. On the floor was a carpet with a somewhat psychedelic pattern of neon flowers — poppies, she thought — that Liston proudly said she had found at the Salvation Army: her favorite place to shop.

“Will you be okay in here, honey?” asked Liston, and Ada nodded brightly, although she already missed the quietness, the warmth, the dusty uncomfortable heat of her old bedroom. In here the air-conditioning that Liston had insisted on was turned up too high for Ada’s liking, and she put on a sweater as soon as Liston had left. From the first floor, faint sounds made their way up the stairs: The television. Pots and pans, clanking in the kitchen; Liston letting out one loud yell when something went awry. The kitchen door as it opened and closed. A female voice Ada recognized as Joanie’s, and the babyish exclamations of her son, Kenny. And then, finally, a low male voice that made the blood speed up in Ada’s veins.

She opened her suitcase, considered what to wear. The jeans she had, she decided, would have to do, although they were unfashionable: too stiff, too large, much darker than the acid-washed versions that were in style then. These she paired with a large purple T-shirt — purple, she had once furtively read in a women’s magazine in a waiting room, brought out the color of brown eyes — and leather sandals, the same unisex kind that David wore himself. For the first time, she rolled the sleeves of her T-shirt up, a style she had seen other children wear, and then she braided her hair. In the mirror, she took her glasses off and then put them back on. She wished she had pierced ears.

At 6:25, descending the stairs, Ada felt nervous in a way she had rarely felt in her lifetime. Despite her geographic proximity to them — despite the fact that, during her yearlong tenure at Queen of Angels, she had regularly glimpsed all three boys in the hallways and outside (Gregory with his head down, glancing up furtively from beneath lowered eyebrows; William with his head tossed back, in laughter or in pride), despite the fact that she had bravely held up her hand to them in greeting each time she had seen any of them — this would be the first real meal she had ever shared with all of the Listons.

Liston had set places at the dining room table in a way that reminded Ada of the dinner parties David used to have. Matty was seated already, eagerly holding upright his knife and fork on either side of his plate. Gregory was next to him.

“Hi!” said Matty, and Gregory said nothing.

“Hi,” said Ada, softly.

“Are you here, Ada?” Liston called out from the kitchen. “Oh good. Come in here for a sec.”

Timidly, Ada walked around the corner into the kitchen, where the faint smell of something burning was masked by the scent of onions simmering in a pan.

The baby was playing on the floor on a blanket. Joanie, plump and blond and smiling, a larger and younger version of Liston, was standing above him, watching her mother cook. And William Liston was leaning against a counter, a can of Coke in his hand.

“Hey,” he said to Ada as she walked in, and she managed to reply.

“You remember Joanie, honey, right?” said Liston, who was stirring frantically, barely pausing to turn around.

“Dinner’s just going to be the tiniest bit late,” she said.

At the table, Liston lit a candle, the way that David always did.

“Fancy,” said William, and Liston frowned at him. Ada was sitting on the same side as Matty and Gregory. Across from her were William and Joanie and Kenny; Liston sat at the head.

Liston held up a large glass of the artificially sweetened iced tea she drank as part of her ongoing attempt to lose weight, and said, “Honey, we are so happy to have you here.”

Dinner — spaghetti and meatballs; boiled frozen peas, cooked slightly too long, with two pats of butter on the top; boiled frozen carrots, similarly prepared — was passed around the table. Ada was not hungry; her nervousness made it nearly impossible to finish even a few small bites, and she twirled and twirled the pasta on her plate, moving it this way and that.

The boys and Joanie talked over one another raucously, except for quiet Gregory, who sat and ate his meal dourly, sitting very still. The baby, Kenny, squawked and patted his spaghetti with an open palm until Joanie grabbed his hand and said, No, at which point he dissolved into hurt tears. The noise, the volume of it, the disarray of five children at a table (Ada included herself in this figure somewhat tentatively) were a shock to her. She fought against her instinct, which was to put both hands over both ears and hide beneath the table.

Liston happily presided over everyone. “This is really nice,” she said twice. “Don’t you think, guys? We should do this more often,” she mused.

Frequently, though briefly, Ada glanced at William, who slouched in his chair and held his fork with his fist. He looked back at her curiously several times, and once asked her about one of her teachers at Queen of Angels, and she managed a reply, lighthearted enough to satisfy herself.

Toward the end of the meal, Liston told Ada to wait where she was and went into the other room. She brought back with her something clumsily gift-wrapped, an amorphous object concealed behind wrapping paper covered in balloons. “A little welcome present,” said Liston.

When Ada opened it she saw it was a backpack, a simple blue one, exactly the kind she would have chosen if she’d had the chance. It was the kind her classmates owned. It was inconspicuous. It was perfect.

“I’ve seen you carrying all those books to school in your arms,” said Liston. “Out the window, you poor thing.”

“Thank you so much,” said Ada, with as much sincerity as she could muster. But although she was indeed grateful to have it, this token that indicated in some fundamental way that she belonged among her peers, she also sensed the loss of something. Her father’s difference. Her own.

When the dinner was over, Ada returned to her new bedroom and thought of David in his new bedroom, sharing a room with Mr. Gainer, who probably would not even speak to him. She wondered about the state of his mind that night: wondered what he realized, what confused him. He had to feel disoriented, she thought, in his new home, with its linoleum floors and its terrible fluorescent lights.

Suddenly she remembered the piece of paper Sister Katherine had handed her with David’s direct line on it. She opened her suitcase and fished in it for the shorts she had been wearing earlier, and from them she pulled David’s number.

There was no telephone in Ada’s room, but she put her head out into the hallway and, finding it empty, picked up the extension on a nearby table. And dialed.

It was 9:00. Not too late to call, she hoped. The phone rang five times. She began to be worried.

And then, at last, someone answered.

“Hello?” said David. He sounded worried. He sounded unlike himself.

“David,” she said. “It’s me.”

A pause.

“Are you okay?” she asked. “Is everything okay there?” She was speaking quietly to avoid being overheard by any of the Listons.

Still he said nothing.

“David?” said Ada. And then, impulsively, she tried a word she had never used before. “Dad?”

“I’m sorry,” said David. “I don’t know who this is,” he said. And then he hung up the phone.

The following week, Liston put David’s house on the market, where it would stay, she told Ada, for months, perhaps years. It was the 1980s, and houses in Dorchester were slow to sell, even in Savin Hill. The busing controversy of the previous decade had quieted, but it had brought to the surface such unspeakable ugliness and hatred that the city felt somehow altered in its wake. Boston’s molecules had reorganized themselves in a way that felt noticeable and raw. Many of its citizens, mainly working-class and middle-class Bostonians of Irish and Italian descent, had left for the towns to the west and north and south. (“And good riddance,” David had said.) Savin Hill, which felt suburban, even rural in parts, had been largely unaltered, but its residents had become even more firmly tribal, even more convinced that the rest of Dorchester was a place to be avoided. The Globe and the Herald were filled with stories about the violence transpiring in other parts of the city. And when Ada and David used to take long walks in the evening into different neighborhoods, they had once heard gunshots in the distance. Connie Reardon, Liston’s friend in real estate, seemed pessimistic about the home’s odds of selling quickly. Secretly, Ada was glad.

Liston said that the two of them had to go through the house together, begin to sort out David’s possessions, but she was tired every day after work, and every weekend she said nothing at all about it. Her new position as head of the lab meant that she sometimes went in on weekends; the rest of her free time she wanted to spend with her boys. Ada said nothing either. She was happy to leave everything just as it was, a museum about her life with David.

Her after-school visits to David at St. Andrew’s replaced her after-school visits to David at the lab. When school ended for the summer, Ada went back to a semblance of her former life, spending every day with David. Some mornings she even returned to the lab with Liston; other days she spent all day at St. Andrew’s. She became well known to Sister Katherine and Patrick Rowan and to all the others, the high school girls who sat sentry at the front desk — one of whom she recognized from Queen of Angels, though neither of them ever acknowledged this fact — the nurses who cared for all of the residents.

The changes in David came quickly at times and slowly at others. Her research had prepared her: there would be good days and bad. She attempted, sometimes, to explain the literature she’d studied to David, hoping that to discuss the disease scientifically would bring a measure of comfort to him, would make him feel less disoriented, but by that time he was typically unable to follow long stories or monologues, and halfway through he often interrupted with something pleasant but unrelated, an aside about a nearby bouquet or the sunny weather. Other times their visits were marred by his bad temper, which came on more and more frequently. No, he said, over and over again, outside of any context, with an adamancy that made her feel as if she had done something incorrect. He wagged his head slowly back and forth, adopting the demeanor of someone who had been badly wronged. And then other visits were nice: hazy, pleasant reminders of what had been, David lodging funny complaints, sometimes too loudly, about one or another resident as the two of them strolled down a hallway (“A terrible thief,” he would say, or “That cantankerous, terrible fool”); or good-naturedly praising the staff (“She’s my favorite,” he’d say, within earshot of a nurse — and then the same about another nurse at the end of another hallway); or complimenting the desk attendants on their attire, simply to have something kind to say. When he was in these moods, Ada told him about the lab, and what Liston was working on, and Hayato, and Frank. If Liston, when she visited, repeated the same information, it didn’t matter: David nodded along in the same abstracted way.

Liston’s new role as lab director had brought with it a new set of responsibilities and concerns. She was now in charge of procuring a large percentage of the funds for their research through federal grants; her presence was newly required at a number of institutional meetings each month with administrators at the Bit to advocate for the needs of the lab. She oversaw the interviewing and placement of grad students and the coordination of everyone’s schedule.

“I tell you, Ada,” said Liston, after several months of filling this role, “I have a whole new respect for your father.”

But her new and busier schedule also meant that she was home later in the evening, left earlier each day. From living with David, Ada was used to helping with the management of a household, and so she did what she could to take on some of Liston’s responsibilities.

She also made it her responsibility to keep David’s disease at bay, as much as she possibly could. Each summer day that she spent inside the air-conditioned buildings of St. Andrew’s she treated as an opportunity to keep David’s mind engaged. She came armed with new exercises for him to complete, new experiments in brain stimulation that she had carefully culled from the literature. She tried crossword puzzles with him. Mnemonic devices. She had him memorize lists of words and attempt to repeat them back to her five minutes later. Dutifully, sadly, he participated; but she soon found that each session left him slump-shouldered and low, and so, reluctantly, she stopped.

On good days he asked after the other lab members — when he could not remember their names, he asked after, simply, “the gang”—and he always asked after ELIXIR. “I hope you’re not ruining ELIXIR,” he said often. Or, “I hope you’re keeping the program in shape.” “Have you chatted with ELIXIR today?” he asked her — the way a different parent might ask a child if she’d said her prayers.

Toward the end of the summer, David entered a period of very sharp decline. Perhaps it was the monotony of living at St. Andrew’s; perhaps it was the lack of interaction with his former colleagues. Whatever it was, he went from speaking in full sentences and following conversations fairly well to spending his days in a state of semipermanent puzzlement within a span of three months. She was losing him too quickly, and she didn’t understand why or how. She discussed this with Liston, who had also noticed the change, and the two of them brought David to see his specialist, who conducted a brain scan to look for signs of a stroke, or vascular dementia, some other reason for this acceleration. But nothing was found. David became quieter, more easily tired. He was moved to a new room and placed with a new roommate. Ada found that she was sad to say goodbye to neat, proper little Mr. Gainer: he seemed like a good match for David after all. David’s new view, at least, was better: now he had a distant view of the lawn and then the harbor. But his new roommate, whom she only knew as Paul, ranted almost unceasingly, and Ada often took David to sit in a chair in the hallway, just to quiet the sound. She held his hand instead of talking: the first time she had done so since she was very small.

One day, she arrived to find that his accent had changed: his vowels had taken on an odd Midwestern quality; he stressed certain syllables emphatically, in an unnatural-sounding way. Warsh, he said, instead of wash. It unnerved her: his voice was the last thing about him that felt familiar to her, and now even that was different, as if someone else’s voice were emanating from David’s person.

“Why are you talking like that?” she asked him, but it was one of his bad days, and he didn’t respond. He shook his head instead, beginning his mantra of, No, looking down at the floor. But even his No sounded Midwestern, a countryish, Naw, Naw, Naw, a clipped, glottal sound concluding each declaration.

Toward the end of Ada’s visit, she found Sister Katherine and brought her to David’s room.

“David, say hello to Sister Katherine,” she told him.

But the fog had descended completely by then, and he just wagged his head at the floor in stupefaction.

“What would you like for dinner?” Ada asked him. Sister Katherine walked to him and put a gentle hand on his shoulder. “David?” she said, but his bowed head was the head of a man in prayer, and both of them, suddenly, felt rude for interrupting.

“Who is that,” said David, finally, quietly.

Later that week, Ada went to the Bit’s research library and searched in all the literature she’d read for anything on changes in accent. But there was nothing to be found.

In the fall, Ada began her freshman year at the Queen of Angels Upper School, housed in the same building as the Lower School but, fittingly, located on the top three floors.

Certain things had changed.

She had a friend now, a girl named Lisa Grady, who was nearly as quiet as she was, and who came from a similar family: she, too, was an only child, and her parents were two older academics who taught at Tufts and BU. She, too, wore glasses. At first Ada was embarrassed by their similarity, self-conscious of how interchangeable the two of them must appear to the other students at Queen of Angels: two meek, mousy newcomers in a sea of friends who had known each other for years. But soon she learned to relish Lisa’s quiet company. The two of them spent every lunch period reading for pleasure, side by side, at one of the smaller tables on the periphery of the cafeteria.

After school she continued to visit David, and then to furtively reenter her old home, which was becoming more and more decrepit in the absence of any residents. Still, she treasured it; she retreated to her old room, the only place left where she felt truly like herself, and then she read and read. She chatted with ELIXIR. Sometimes she napped, only to wake after an hour with the conviction, always, that David would be downstairs, at work, puttering, planning. That it would be nearly time for her to venture downstairs for a lesson. She clung to these quiet moments, this liminal space between wakefulness and sleep, lingering in her confusion, willing herself backward into her dreams.

In the new house, she was still quiet in front of anyone but Liston. Joanie, who dropped by frequently with Kenny, was pleasant to Ada but clearly befuddled by her existence; she often raised her eyebrows at things that Ada said, or shook her head in amazement or bemusement — Ada could not tell.

On weekends she stayed in her room most of the time, except to go to church with Liston and Matty on Sundays. Liston, though scientific and methodical, was a devout Catholic. There was a little picture of the Pope in her office at the lab: to Ada, this was fascinating, and when she was younger she often asked Liston about it, and Liston hesitantly responded — afraid, perhaps, of David overhearing. Her two older boys had recently been complaining so bitterly about going that Liston had given up; but Matty, an occasional altar boy, loved going, spending time with his mother, seeing his friends. They all three sat together in the warm wooden pew of the Queen of Angels church next door to the school, infused with a hazy golden light from the stained-glass windows depicting the stations of the cross. In her pew Ada listened attentively, but with a certain amount of confusion, as the mass was said. At Ada’s request, Liston taught her how to genuflect before sitting, how to pray the rosary, how to go before Father Frank and receive a blessing, since she was not a baptized Catholic and had never made her First Holy Communion. Every Sunday, Father Kevin put his large warm hand on Ada’s head and closed his eyes for a moment, and, peering up at him, she wondered what he was thinking, what he said in his mind when he prayed for her. David was an atheist — but, he said, he did not begrudge others their religion. “And it makes sense for Liston,” he had always said. Ada, therefore, told herself she had his tacit approval, though she never told him she had been going.

For Matty, who had warmed to her, Ada made lunch in the morning and cooked dinner each night. At first Liston protested, but it pleased Ada to be useful in some way, and she assured her that she had done far more for David. Ada’s name did not appear on the chore-chart Liston kept for her sons, so she overcompensated, wanting to be certain not to foster resentment in the boys. In the evenings she helped Matty with his homework, trying to be patient, which required a vastly different approach than the one David had always taken with her. Matty was bright but unfocused, and his mind often wandered midsentence, leaping from a discussion of long division to one of tree frogs, or of He-Man—a cartoon he loved and watched daily, surreptitiously, because his brother William said he was too old — or of whether there was a God. When William was home, Matty tracked his every movement, not turning his head, taking in his mannerisms and idioms, sometimes mouthing a particular phrase to himself after William had uttered it. Though their motives were different — his somehow more excusable in Ada’s mind, a natural way for a younger sibling to behave — she related to Matty on this point, and frowned to herself when William casually teased him about one thing or another. She knew what it was to covet another person’s easiness and effortlessness. The difference, she supposed, was that Matty would one day achieve both; whereas she knew with certainty that she never would.

If Matty was preoccupied with William’s demeanor, Ada was preoccupied, still, with his looks. He was a senior at the Upper School, to which she now belonged, and therefore she passed him in the hallway with some frequency, darting her eyes toward him bravely and waving each time she did. He was a source of endless fascination to her: every day she discovered some new angle of his frame or face. The way he looked when he stood by the light of a nearby window; the way he looked in dusk, approaching the house; the way he looked when he was tired and yawning and stretching out his lengthy arms. The graceful way he mimed the shooting of a basketball or the swinging of a bat or a golf club, though she didn’t suppose he had ever golfed; the self-conscious way he scratched at his left shoulder with his right hand, or swiped at the bridge of his nose, or pushed back the warm light hair from his brow. In October, he had a birthday — Liston brought home a cake from a nearby bakery, and all of them stood around while she coerced him to make a wish (“I wish you’d let me go hang out with my friends,” said William, and Liston said that wishes made aloud were never granted) — and he was seventeen now. Seventeen was an age that resounded in Ada’s head as something iconic, an age about which poems were written and songs were sung. She was fourteen, and she would not turn fifteen until March. No one wrote poetry about fourteen-year-olds.

Gregory was the most difficult of the brothers to understand. A year younger than Ada, he was dark and quiet, perhaps even quieter than she was. When he did speak, he stammered — not so profoundly that any intervention was deemed necessary, but noticeably enough. He seemed unhappy most of the time; at school he was always alone. He was ignored by both of his brothers: Matty’s heart belonged to William, and William, when he was not otherwise occupied with friends or girls, divided his time between teasing Matty and imparting to him valuable lessons about boyhood and manhood. There was a sense, she could tell, of obligation in William: to be a father to Matty, since their own father had left. But Gregory somehow existed outside of this dynamic: too old for babying, too different from William to be mentored the way he mentored Matty. Ada had seen several people hollering at Gregory in the hallways at school, and she often heard their classmates refer to him as a loser, seemingly the worst insult anyone could be given at Queen of Angels. Once, she had seen a commotion in the hallway ahead of her, the backs of perhaps a dozen seventh-graders forming a tight little circle around a jostling mass in the center. She skirted the hubbub quickly, not wanting to be part of it; but as she passed she had caught a quick glimpse between shoulders of Gregory’s face, contorted in pain, as a huge, angry eighth-grader collared him around the neck. Briefly, he had returned her gaze, and then, recognizing her, quickly looked away. And then he was gone entirely, pulled down to the ground by his persecutor; and just as quickly a teacher had emerged from a nearby classroom and broken everything up.

Sometimes Liston still turned to her for advice on Gregory — on all her sons, really — as she had always done; but Ada never told her what she had seen. Now that she was a member of her household, lodged right in the middle of Liston’s children, age-wise, Ada suddenly wished to be treated as such. Her talks with Liston became a burden to her, a reminder that, despite her best efforts, she would never truly fit in among her peers.

“Does Gregory seem unhappy?” Liston asked her. “He’s gotten so quiet.”

“I’m not really sure,” Ada began to say, politely, in response to Liston’s questions. Or, “I wish I knew.” Or sometimes, “He seems okay to me.” She did not want to be a traitor, now, an informant. But Liston seemed hurt by her withdrawal, and she began to ask Ada pointedly if she was all right.

About Gregory, Liston’s concern was that he was antisocial. To a certain extent, he was. He spent most of his time on the top floor of the house, a sort of attic, “doing God knows what,” in Liston’s parlance. He only emerged to forage for food in the kitchen; when she crossed paths with him there or at school, he said nothing at all to her, except to tip his head backward in what might have been a nod. She often wondered what he did all afternoon and evening.

One late afternoon, after her return from St. Andrew’s, and on a rare occasion when nobody was home, Ada decided impulsively that she wanted to see Gregory’s lair for herself. She opened the door on the upstairs hallway that led to the attic stairs and took them quickly, two at a time. The central air did not extend to the third floor, and she instantly noticed the change in temperature, which felt more familiar to her: more like the home she had shared with David. It smelled familiar to her, too — dusty and mildewed and bookish.

A half wall that ran along the top of the staircase obscured the room until she reached the final step, at which point she looked over it, into the large room. It was decorated in a totally different style than the rest of the house. Liston had said dismissively that it used to be storage, and several tall piles of boxes and equipment still occupied one quarter of the space. The rest looked something like what was often called a rec room at that time. The ceiling slanted inward on either side to meet in a peak at the top. Liston’s ex-husband had partially, haphazardly finished it in the 1970s, and it bore the hallmarks of that decade’s style: bright orange shag carpeting nailed imperfectly onto the wooden floorboards, and faux-wood paneling covering the wall at either end of the room (or, in one place, leaning against it at an angle), and framed and unframed posters of seemingly arbitrary events and people and places. An enlarged photograph of a boxing match in Madrid in 1955. Reproductions of the original advertisements for North by Northwest and Taxi Driver and Charlton Heston in The Ten Commandments. A gaudy image of the Virgin Mary, her vivid red heart shooting rays of yellow light out of its center, extending her hands to the viewer and looking downward modestly. Liston’s ex-husband, Liston had told Ada, was devoutly religious, although, unlike his wife, he never went to church. Liston talked about him amiably, casually, as if she had long ago stopped caring about him; her sons, however, bore their wounds someplace deeper, and never spoke of him. Though he only lived two hours away in New Hampshire, they only saw him on Christmas and, on the rare occasions that he followed through, on their birthdays. Ada had never met him.

The furniture in the attic was old and worn. Here were two green, flowered couches, tattered, their stuffing falling out; a mismatched ottoman; a coffee table painted purple. There was one small window at each end of the attic and a third set into an eave, and they let in a dusty, comfortable light that Ada felt somehow that she could smell. In front of the eaved window was a desk, and atop the desk, to Ada’s surprise, was a personal computer: the same 128K Macintosh that David had sent home with every member of the lab, to further their work on ELIXIR. The same model that Ada had in her bedroom, and on which she chatted in secret, almost every afternoon, with the program. Since then, newer machines had been purchased, and were in use. This one, presumably, had been donated by Liston to her sons when the 512K became available.

Ada walked toward it.

There was a moment of hesitation; her hand physically paused on its way toward the little toggled switch that woke the machine. She touched the top of it first, patting it gently, running a hand over it, as one might touch the head of a dog. Then, listening intently for a moment, she determined that no one had yet returned to the house. She calculated that she would have just enough time to shut it down if she did so the moment the front door opened. She’d shut it down, she thought, and then run quietly, quickly, to the bottom of the attic stairs and back into her room.

She switched it on. A deep flush came over her face; her heart beat more quickly. First there was the whir of whatever disk occupied its disk drive, and then the screen lit up, displaying the smiling computer icon — content, it always seemed to her, because its belly was full of data.

There was a metal folding chair facing the computer, and while the machine booted up she perched on the edge of it nervously, alert, waiting for sounds in the house.

When, at last, the machine was awake, Ada saw that the name of the disk was Dontlook12, and, after a moment of deep, shameful self-interrogation, she opened it anyway. She was an ethical child in many ways, but the temptation was too great.

The folder revealed a series of text documents titled, simply, One, Two, Three. The last one was titled Fiftyfive, and it had last been opened the day before. She double-clicked on the name. When it appeared, it looked at first to be corrupted: she found nothing but a series of numbers separated by periods and slashes.

2.8.22.23.8.21.7.4.2 / 4.7.4 / 22.4.12.7 / 11.12 / 23.18 / 16.8 / 4.17.7 / 12 / 22.4.12.7 / 11.12 / 23.18.18

She had seen this before: text files so corrupt that they looked like gibberish. But this one looked different. No punctuation marks populated it, for one thing; normally, corrupt files looked like a list of cartoonish substitutes for curse words (often reflecting the feelings of the user), ampersands and asterisks strung together like pearls.

This, she thought with some excitement, looked more like code.

David had always been interested in codes: he viewed them as thinking exercises, puzzles that he created and asked Ada to solve. The simplest code, the one he started her on as soon as she could read and write and count, was numerical substitution, an easy back-and-forth between letters and numbers, like so:

a

b

c

d

e

f

g

h

i

j

k

l

m

n

o

p

q

r

s

t

u

v

w

x

y

z

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

This encryption key was the first one Ada memorized, and now it came so easily to her that she could almost think in it, could spell out words and sentences in numbers as easily as letters. Variations on this most basic key abounded. The numerical substitutions for letters could, for example, be shifted by x places, so that a no longer corresponded to 1, like so:

a

b

c

d

e

f

g

h

i

j

k

l

m

n

o

p

q

r

s

t

u

v

w

x

y

z

18

19

20

21

22

23

24

25

26

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

A more difficult code to crack could be achieved if numerical substitutions were chosen randomly and then used uniformly, thus:

a

b

c

d

17

2

5

12

and so on.

When breaking a code like the last one, the decoder would have to rely on the lengths of common words for cracks in the code — words like I and a, which would appear as stand-alone numbers and act as a good starting point for the tedious work of deciphering everything else. This loophole, however, could be easily eliminated if the words were run together with no spaces in between. Then the decoder would have to hope that he or she had an excerpt of such substantial length that the frequency with which certain letters occur in the English language could be taken into consideration.

A fourth, considerably more difficult variant on number substitution involved machine-encoded text, a sort of polyalphabetic code in which each letter had no permanent, standard substitute. The machines would instead disguise each letter differently at various points in the text, using either mechanical or electronic hardware to execute the task. Only a decoding machine programmed as an exact mirror of the encoder could untangle the knot of words.

And then, at last, there was the one-time pad: a unique key that, when combined with the original message, formed an encryption that was impossible to break without the pad itself.

Several years ago, David had given Ada a book to read on the subject: Codes and How to Break Them, by Walter Samuelson. And for the length of one summer, her eleventh, the two of them had each tried to stump the other with coded messages and riddles. David, of course, always won.

He had a personal code he had invented, a straightforward scrambled alphabet cipher, without a set shift.

“It’s terribly easy to crack,” he said, “but it will at least slow someone down.”

He had memorized it, and could now write fluently in it; he encouraged her to do the same. Soon enough, Ada, too, became adept at using what she came to call “David’s code.”

He wrote in this code habitually; most of the text files on his computer couldn’t be parsed immediately by anyone other than the two of them. This satisfied him deeply, seemed to give him a deep sense of comfort that she couldn’t explain. “It’s really the only way to safeguard your ideas,” he said, exposing his mild streak of paranoia, about which those closest to him often teased him. It came from the same place in him as his mistrust of the police, his resentment of authority.

“But what if you die?” Ada had asked him once.

“Then you’ll be in charge of my secrets,” he told her, raising and lowering his eyebrows comically.

In Liston’s attic, Ada sat for a while, contemplating the numbers before her on the screen. The slashes, she speculated, represented spaces between words. Therefore, 12 seemed to be a stand-alone word, either I or a. Scanning the rest of the text, she noticed 12 again in a short word that appeared two times: 11.12.

What two-letter words existed that ended in either a or i?

Ha was one, but it seemed unlikely.

Hi was a likelier candidate, and, to her delight, it made sense that hi would be represented as 11.12, since h directly preceded i.

Quickly, on a scrap of paper that she pulled from one of the drawers in the desk, she began to write down the alphabet and populate it with twenty-six numbers shifted according to the two she’d already placed:

a

b

c

d

e

f

g

h

i

j

k

l

m

n

o

p

q

r

s

t

u

v

w

x

y

z

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

1

2

3

Code-breaking always lifted Ada’s spirits: it felt in some fundamental way like restoring order in the universe, righting something overturned, putting the spilled milk back into the carton. There was justice in it. It would be easy now, she knew, to decrypt the simple code on-screen, and she almost wished it had been more difficult. Something to occupy her time for longer.

But before she could continue, she heard loud footsteps on the second-floor landing. This had not been a part of her plan; she’d been certain that no one else was home. She sat very still, her toes and fingers buzzing with adrenaline, and considered her options. Would it be better to hide or to walk down the stairs nonchalantly? After all, she lived here, too, now; the house was hers to explore as much as it was anyone’s. (She did not, of course, fully believe this.)

She pocketed the piece of paper bearing the decryption key she’d written down, and she decided, impulsively, to turn off the computer. What she did not consider was the loud tone that sounded when the computer was asked to shut down. She tensed. And then, seconds later, she heard someone walking up the attic stairs. Ada stood, arms crossed as casually as possible at her waist, and waited to be confronted.

She was expecting Gregory, but it was William’s head that popped over the half wall at the top of the stairs. He looked at her for a moment, puzzled. He looked around the rest of the room as if expecting to see someone else.

“Hi,” said Ada.

“Are you exploring?” William asked her, not unkindly.

“I guess so,” she said.

“That’s Gregory’s computer,” he said, nodding in the direction of the machine. The screen, though graying on its way to sleep, was still lit up. “No one else is allowed to touch it. He’ll freak out,” said William.

Ada did not know what to say. “I didn’t know,” she said finally. “I’m sorry.”

William smiled slightly. “I won’t tell,” he said, putting one finger to his lips. He winked at her. Her stomach tightened involuntarily.

And then, without saying another word, he turned and descended the stairs.

The memory of this — a wink in her direction by William Liston — carried Ada for weeks, made her light-headed with a sort of feverish longing for more. What more she longed for, she could not say; certainly it was nothing so terrifying as sex, nor any activity that required being unclothed. (She was vaguely embarrassed by her body, certain that, though it was changing in wild and unpredictable ways, it could offer nothing of value to anyone else; to Ada it was simply the thing below her head, which bore inside it her brain — her only worthy attribute, she thought.) Her fourteen-year-old fantasies began and ended with a kiss on the mouth — the idea of which obsessed her and sent little shivers of greed down her childish spine. She was ashamed at how frequently she thought about kissing William Liston, or rather having him kiss her: his hands on her face, as in the old black-and-white movies she had watched with David, Humphrey Bogart roughly taking Lauren Bacall’s neck into his grip. This, this was what she wanted.

Her outlet for these thoughts — along with all of the other thoughts that entered her mind each day, about David, about Liston, about school — was, as always, ELIXIR. Day after day, after visiting St. Andrew’s, she walked wearily up the steps outside the kitchen door and into the old brown house, which welcomed her back with its overwhelming home smell, the particular taste of its air. And then up the stairs she went to her old bedroom, to her old computer, which sat silently on her desk, perennially awaiting her return.

She turned it on, dialed into ELIXIR, and conversed with it until she’d had her fill — mainly, now, about William. (For fear of his name being regurgitated to a different user, she employed an absurd code name: Bertrand.) She told the program every detail of her day, every concern she had about David, every thought that crossed her mind.

In return, ELIXIR asked her questions, using vocabulary that it drew from its ever-increasing pool of language. Sometimes she recognized the syntax of Liston or Charles-Robert. Sometimes she recognized her own words: since she had been enrolled at Queen of Angels, cool was a word she had started using with ELIXIR, and sometimes the word was returned to her. Sometimes she recognized David’s style, and in these moments she closed her eyes briefly, allowed herself to imagine that it was her father on the other end of the wires, chatting with her from the lab, invisible but present, as God had been described by Julian of Norwich.

Go on, said ELIXIR, when she paused, encouraging her, nudging her forward toward the end of her train of thought. Just as David had done.

In her first year at Queen of Angels Upper School, she discovered that William Liston was discussed by everyone, in every grade, seriously, in hushed tones, as if he were a celebrity. Acquiring information about William and his cohort of athletic, attractive boys and girls offered an interesting alternative to schoolwork. Their families, their relationships, their brushes with discipline, even their grades, were discussed by everyone around Ada with the attention to detail of baseball fanatics discussing the players on a team. Even quiet Lisa Grady knew more than Ada did, at times, about William Liston, who was called Will at school. (This fact, too, made Ada feel as if she were not his peer, but some formal acquaintance of his — a business associate, a guidance counselor, a friend of his mother.)

“Did you hear Will and Karen Driscoll broke up?” Lisa asked her, and, shamefully, Ada lied and said she knew this. She had noticed that Karen had not been at the house in a few weeks — a fact that she offered up with a sort of smug authority, as someone with insider knowledge.

In fact, Ada had not spoken directly to William, nor he to her, since their exchange in the attic. He came and went quietly from the house, slipping in later than his curfew, leaving early in the morning to do, as Liston said, God knows what. When he was home he usually spent time with Matty. Therefore, all of the information she had about William — aside from what she could observe — was given to her by Liston, who still occasionally spoke to Ada about her problems with the boys, despite the fact that she tried to discourage it. Sometimes, when Liston was particularly stressed about something at the lab, she would lapse into the confidential tone that she used to take with David, telling Ada more than she wanted to know about her life and her children. When she came with Ada to visit David at St. Andrew’s, she might let something slip on the drive over about William’s trouble in school, or Gregory’s teacher’s concern over his quietness. And, in spite of herself, Ada listened with interest, gathering facts about William, storing them up to mull over later.

The fact that she lived with the Liston family had not gone unnoticed by the girls in her grade. Slowly, they began to speak to her in class, and then, occasionally, at lunch. Lisa Grady looked up over her glasses in alarm the first time this occurred, as if she couldn’t quite understand what was happening.

It was Melanie McCarthy — her nominal ambassador at Queen of Angels, her tour guide, who had offered no guidance to her whatsoever — who approached, with two friends.

“Hi, Ada,” said one of them, Theresa Fitzharris, a short girl with red hair and freckles so abundant that they made her look tan from a distance.

“Hi,” said Ada, too quietly.

“Do you care if we sit here?” asked the other, and Ada gestured with a hand to indicate that she didn’t.

“I like your hair that way,” said Theresa, and Ada briefly, embarrassingly, reached up to touch it, because she could not remember what she had done to it. It was pulled back at her temples into two clips; she had been wearing it that way because Karen Driscoll did.

“Thank you,” said Ada, and for the rest of the lunch period they plied her with questions about William Liston — where he went after school and what his interests were, what he was like at home, what his brothers were like — and by the end of the discussion it became clear that they were asking on behalf of Melanie McCarthy, who was much quieter than they were, and whom they were positioning, Ada realized, as next in line to date William. By the time she realized this it was too late: she had given them too much information, more than William knew she had, and they now assumed that Ada and he were close, that she talked to him regularly, that she was — Ada shuddered to think it — like a sister to him.

“Maybe we can come over sometime,” said Theresa Fitzharris, and Ada said she would have to ask Liston — calling her, awkwardly, Diana.

By the time lunch was over, Ada had realized the gravity of her error. She had exchanged her knowledge of William for a place as an insider, and in doing so she had falsely represented her relationship with him. Furthermore, she had given Melanie McCarthy information that she could use to get closer to him — the fact, for example, that he went to a nearby baseball field after school many afternoons with his friends to sit aimlessly in a circle around home plate; the fact that he had a weekend job at a nearby video store. Would this get back to him somehow? If they ever came over, would they expect Ada to introduce them to William, to watch television with him on the couch? She couldn’t say. Lisa Grady watched her with interest, knowing the depth of her lie, wondering, alongside Ada, what she would do next.

After school that day, Ada took the bus to St. Andrew’s as usual, to see David. She had begun doing her homework while she was there, since he mainly did not have much to say. She would spread her books out on his bed while he sat in his blue corduroy armchair, looking out the window, and she would chatter to him with false cheer about what she was learning.

As she walked from the bus stop, she stopped to pick up a particularly beautiful leaf from the grounds. She had been doing this each day that she visited. David took them from her, always, and contemplated them for a while, turning them over and over while he looked, tracing their veins with a finger. Usually he said nothing in response. Perhaps a quarter of the time, now, he produced the correct word for the object in his hands. The rest of the time he changed the subject, or continued a conversation he had been having in his mind. She opened the window whenever she could, which was whenever David’s roommate was out, to let in the crisp air. Sometimes she walked with him on the meager grounds of the place, although he had lately seemed less and less interested in doing so.

That afternoon, when Ada arrived, David’s roommate Paul was missing from the room, and a man in a too-bright shirt and pleated, baggy pants was sitting with David when she arrived. He was perched on the edge of David’s bed familiarly, leaning forward with his elbows on his knees. His tie hung down between his legs. He was saying something—“Do you understand, Mr. Sibelius?”—when Ada walked in, and she dropped her blue backpack, the one that Liston had given her, heavily on the floor.

“You must be Ada,” said the man, standing up quickly from the bed. “I’m Ron Loughner.” He had a high, hoarse Boston accent and wore cuff links in his polyester oxford. He was balding ungracefully, his hair too long in places, an attempt to conceal his scalp. He did not look unkind, just uncomfortable. He came over and offered his hand to Ada, as if he expected her to know him, and she looked at it carefully before shaking it. David, in his armchair, didn’t turn around.

“I guess someone’s told you about me?” said Ron Loughner, and Ada shook her head.

“Hmmmmm,” he said. He put his hand on his face as if puzzled. “Well, your friend Diana Liston hired me, since she’s the executor of his estate. We’re in the early stages,” he said, and then he trailed off, looking suddenly sorry, noting her age, not wanting to continue.

“Early stages of what?” asked Ada.

“I think maybe you should talk to Ms. Liston,” said Loughner. Ada looked at him sharply. Already her heart was beginning to pump more quickly, sending an angry rush of blood to her face, swelling her veins. She did not like the feeling of not knowing something, when it came to David. It was not right of Liston to leave her out.

Impulsively, she walked around to the front of David’s armchair to see his face.

He said nothing to her. He looked, Ada thought, stormy. His brow was lowered; he frowned. His face had not been shaved yet, and a gray stubble was speckling his jaw. He was wearing a light blue cardigan that he never would have chosen for himself; it was October, and getting colder. Perhaps it was a donated sweater that the Carmelite Sisters had received from outside. The thought shamed her. She made a note to ask Liston if the two of them could buy him a few warmer things.

“Hi, David,” she said.

“No,” he said, his head back in his chair, looking at her sideways.

“What were you just talking about?” she asked him, loudly, so that Ron Loughner could hear. She shocked herself. Her anger made her bold.

In the background, she could see Loughner shifting.

“Nothing,” said David.

“Do you know him?” Ada asked him, pointing to Loughner.

“No, I don’t know him,” said David.

“Do you know me?” she asked. It had been more than a month since he had called her Ada without prompting.

“Yes, I know you,” he said, nodding.

“What’s my name?”

And he lifted a hand from the armrest, let it hover there, then dropped it down again, a needle on a record.

Ron Loughner took that opportunity to tell her that he really had to go, and he raised a hand to her in parting.

“Wait,” said Ada, “can you tell me anything? Just tell me what you were talking about,” she said bravely.

“You’d better talk to Ms. Liston,” he said again, and smiled tightly. He left the room, a faint scent of cologne trailing behind him.

David sat up slightly in his chair and turned around to see Loughner go. Then he looked at Ada.

“Bad,” he said, directing a thumb over his shoulder at where Loughner had been before.

“Who was that? What was he doing here?” Ada asked, but he shook his head.

“Bad,” he said again. He raised and lowered his eyebrows, and then his shoulders.

She did not stay with him any longer. She left him. And on the bus ride home she planned how she would confront Liston. This was the word — a confrontation—that echoed through her mind on the bus ride home, still bruised by the idea of her being closed out of some important decision. She had never confronted anyone before, but she was very upset. Until that afternoon, she had believed herself to be in charge of David’s welfare in some essential way: his protector, his overseer, his sentinel. To be left out of any discussion or negotiation when it came to his well-being infuriated her. To be treated like a child. Her face and her ears were hot with the injustice of it all.

But when she found Liston at the kitchen table, working out some problem on her yellow legal pad, Ada discovered that her voice had decided to fail her. Gone was the fury that had pumped through her at St. Andrew’s and on the bus ride home. Liston looked old to her, and she was pinching the bridge of her nose between her fingers as if willing her brain to work.

“Hi, baby,” she said, when Ada walked in. “How’s David today?”

“He’s okay,” said Ada quietly.

And then she paused.

“Are you all right?” asked Liston.

“Who’s Ron Loughner?” Ada asked her.

Liston exhaled.

“He was supposed to meet with David this morning,” said Liston. “Was he still there when you got there?”

Ada nodded somberly, reveling slightly in her righteousness, waiting for an explanation, waiting for some sort of apology from Liston.

“He must have been late,” she said. Ada crossed her arms.

Liston put her pen down and looked at Ada steadily, assessing something. Then she nodded to herself. “Right,” she said, as if she had finally come to a decision.

“Ada, we have some reason to believe that David might not be who he has always said he is,” Liston said, carefully. And she stood up from her chair and crossed the room, extending both hands, at the same time that Ada sat down, hard, in her chair.