The Mammoth Book of the Adventures of Professor Moriarty

Moriarty and the Two-Body Problem Alison Joseph

It seems rather odd now, looking back, that I didn’t see the shape of things. Given that, as a mathematician, seeing the shape of things is what I do, finding order instead of chaos, a pattern where once was randomness. As Professor Moriarty might have said – but, no, I must start at the beginning.

They were happy times. It was a small college in London, and I was embarking on my research under the supervision of Professor James Moriarty. My father, a pharmacist in Norwich, couldn’t understand what had made me leave the security of Cambridge to end up in London, working with someone no one had heard of. But I’m working on Gauss, I tried to tell my parents. Carl Friedrich Gauss, who charted the path of the comet Ceres where everyone else had failed. I knew that Professor Moriarty had been feted in his day for his influential work on the dynamics of an asteroid. And now here he was, tucked away in London, in a small room in St Dunstan’s College, still knowing more about Gauss’s calculations than anyone other than Gauss himself.

‘I can’t imagine why you’ve come to me, young man,’ were his first words when I introduced myself. ‘Once, long ago, I might have had some influence, but we’re in the twentieth century now. My work no longer carries any weight. Where once my name struck fear into my enemies, why now, no one has heard of me at all.’ Then, with a brief, thin smile he said, ‘I have no enemies now.’ His gaze had somehow gone beyond me, into the distance, into the past.

Above him hung a portrait, and my eyes were drawn to it. It was clearly the Professor himself, as a younger man. Even now one could see the similarities. He looked more distinguished, older, of course, but the grey hair was still thick, the same domed forehead, the same rather stiff, upright posture. Next to it there was a charming painting of a boy, sitting at a table upon which lay various mathematical instruments. Moriarty’s gaze followed mine.

‘Le Petit Mathématicien,’ he said.

‘French? I said.

‘Greuze,’ he said.

‘I’m afraid I don’t know who that is,’ I said.

He laughed. ‘It’s a copy. I do have an original Greuze, but in the past certain people made rather, shall we say, unfortunate judgements about me for having such a valuable thing, so I keep it to myself. Now, young man, tell me why you’re so keen to allow an old has-been any kind of influence over your work.’

I began to describe my work. I talked about orbits within solar systems, the measurement of the angle between two planes, and the measurement of the arc intercepted between the poles of the curves, and, as I talked, I noticed how his expression carried a blankness, almost a sneer. I wondered whether perhaps my parents were right, and that staying in the confines of Emmanuel with a tutor I knew well might have been a more rational decision.

But what my parents didn’t yet know was that I had encountered Angela, a lovely librarian who worked in the university and lived with her widowed father in Harrow; and I had resolved that, if staying in London gave me the chance to see more of her, then London it would be. What they also didn’t know was that I had taken a part-time job in a printers’ warehouse in Holborn just to keep a roof over my head. I occupied two small rooms near Chancery Lane, where at night I would lie in bed listening to the rain dripping from the broken guttering and the shouts of unruly law students in the streets below.

I had reached a point in my paper where I describe the calculations for the two points on a sphere that correspond to any given point of the curved line upon a curved surface.

‘Hah!’ Moriarty’s exclamation interrupted my musings. ‘This is all very interesting to me.’ The flickering sneer had gone, replaced by an intense, dark gaze. ‘It’s not often people ask for me by name these days,’ he said. He leaned back in his chair, glancing upwards at the portrait on the wall. ‘Mathematics,’ he said. ‘The purest of the sciences. Gauss charted the path of the asteroid, not by looking outwards at the skies, but by looking inwards at the numbers. That’s what we mathematicians do. We find the glory of the heavens in the pure, abstract truths of calculation.’ He turned to look at me again. ‘The workings of numbers,’ he said. ‘So much more reliable than the workings of the human heart. I shall be happy to tutor you.’

And so began our collaboration.

Moriarty was not a warm person. There was something hidden about him, a coolness, a distance. But his brilliance was indisputable. He was often occupied with his own writings, a reworking of his early work on the binomial theorem. ‘Mere footnotes to Plato,’ he said to me once with a wry smile. ‘The balance between positive and negative, almost Manichean in its dualism.’ Sometimes he’d say to me, ‘Mr Gifford, I’m an old man. It’s 1921. We have a new mathematics, we have general relativity, we have Hilbert and his unsolved problems. Worse than that, we have the legacy of this terrible war, the world turned upside down …’ An air of weariness would cross his face, and his eyes would appear hooded, almost blank. But then something in my calculations would awaken his interest again, and we’d be off, and I would once again be impressed at the quickness of his mind, and his deep love of his subject.

It was a friendly department. The tutors’ common room was oakpanelled and convivial, full of smoke and conversation. There was a fellow who had joined at the same time as me, a young Oxford chap named Roland Sadler, working on quadratic forms, and we used to share a pot of tea together most afternoons. I noticed that Moriarty was rather left alone. One of the tutors, when I said I was working with him, simply said, ‘Poor you.’ ‘Ah,’ someone else chipped in, ‘the arch nemesis, or so he likes to think,’ and there was laughter, not altogether kind. I was glad that the Professor wasn’t there to hear.

The head of the department was a Scotsman, Dr Angus McCrae. Amongst the other tutors was a new star, a woman named Dr Eveline Brennan. She had made her name at Girton, and had worked with the famous Isabel Maddison, teaching at Trinity College Dublin before joining our department. Some of the men were wary of her, but I liked her directness, her disregard for the social niceties. She called herself a New Woman, and rumour had it that she had studied martial arts with the suffragette Edith Garrud. She also was alone in being kind about Moriarty. ‘It’s thanks to him I got this position here,’ she confided in me once. ‘He said he admired my work on c- and p-discriminants.’

One can always see a pattern in retrospect, of course. But, at the time, to a mere observer, the unfortunate events unfolded in a succession that appeared to be entirely random. It all started in such a peculiar way. It was a sunny Monday morning, and we were variously engaged with our teaching, enjoying the sense of spring in the air, when there was a terrible noise from the quad. We ran to the windows to see two men fighting, right in the middle of the neat lawn. Real punches were being thrown, and we could see that one man was getting the worst of it, with a nasty cut across his jaw.

We ran down to the quad, Eveline ahead of us all. ‘Stop that now,’ she was shouting.

‘It’s the college porter,’ someone was saying. ‘Old Seamus.’

‘Who’s the other chap?’

‘No idea.’

‘Stop.’ It was Eveline’s voice ringing out. ‘Stop that. Stop that now.’

Her words had an extraordinary effect. The punches stopped. The strange man was standing, panting, staring at her, his fists clenched at his side. He had a shock of black hair, a cheap ragged jacket. Seamus the porter began to crawl away, one hand across his bleeding jaw.

Still the man’s dark eyes were fixed on Eveline. Then he spoke. ‘I came to find you,’ he said. ‘I’d heard you were here. But I didn’t dare to believe it.’

She was standing, illumined in the May sunlight, upright in her long black skirt, her starched white blouse. She spoke to him quietly, but, as I was nearby, I heard what she said. ‘I thought you were dead,’ she said. Then she turned and strode away into the college, without looking back.

Roland had gone to help poor Seamus. The rest of us stood, awkwardly. The brawling man had slipped away. People began to drift back to their teaching. I was aware of someone standing at the windows above, and I looked up. Moriarty was staring down at the scene. I could see him, framed by the window of his room. And I could see that he was smiling.

That evening I went to meet Angela at the library. We would often go to a little Italian restaurant and I would buy her dinner, even if it meant eating nothing but toast for the rest of the week. This evening she insisted on paying for her own dinner. ‘You’re a New Woman,’ I teased her. ‘Like Eveline. You’ll be learning ju-jitsu soon too.’ Angela laughed in her sweet, shy way, her brown eyes half hidden behind her dark curls. I almost asked her to marry me there and then.

The next morning was damp and drizzly, and the atmosphere in the college was rather muted too. People whispered in corners. Roland told me that poor Seamus was clearly terrified, even though the strange man seemed to have disappeared. Moriarty too was distracted. I had come to show him my calculations on the isometric simplification of the two-body problem, but his gaze was often drawn to his own papers. ‘Dualism, Mr Gifford,’ he said to me, suddenly. ‘In Manichean terms, there is always the opposite. For every positive, the negative. The force that reaches upwards towards heaven is always balanced out by Lucifer, the fallen angel.’ Then he gave a strange, short laugh, reached for my calculations, scanned them with a glance and said, ‘Ah, but you see, remember your Kepler – given that we know the value of “M”, here, you still need to calculate the eccentric anomaly, here …’

And we were off again.

The next odd thing that happened was that later on that morning, while I was still with Professor Moriarty, we were interrupted by a knock on the door and Seamus appeared, carrying a large parcel of papers. ‘These were left at the lodge for you, sir,’ he said.

‘Hah!’ Moriarty seized the brown paper bundle. ‘Very good. How are the bruises?’ he asked.

‘On the mend, thank you, sir.’

‘You knew your attacker?’ Moriarty watched Seamus closely as he replied.

‘Oh yes, sir. Never thought I’d see him again though.’

‘An old grudge, perhaps?’ Moriarty yawned, and his eyes drifted back towards the newly delivered papers.

‘You could say that, sir.’ Seamus, seeing that Moriarty’s interest had waned, gave a brief bow and departed.

Moriarty placed his hand on the papers. ‘An explanation, Mr Gifford,’ he said. ‘I have a brother. Well, I have two, but this concerns my younger brother. He’s a stationmaster in Dawlish. There’s an old family matter outstanding that he’s trying to clear up. He always was the guardian of these things. A mild-mannered, moral sort of man, never leaves the West Country, but he has deemed this business sufficiently important to visit the capital. Our other brother is a colonel and mostly overseas.’ He flicked briefly through the first of the files then turned back to me. ‘Enough. To work, Mr Gifford. Kepler’s equation awaits us.’

That afternoon I went to my paid job. Loading boxes was dull work, but freed my mind for my calculations. An hour or so passed pleasantly enough, until I was amazed to see one of the shop-floor lads appearing, breathless, in my packing station. ‘Your college has sent for you, Owen – they say can you come quickly, a terrible thing has happened.’

I hurried through Bloomsbury, barely aware of the abating drizzle, the thin sunlight breaking through the clouds. At the college lodge, there was a crush of people, and I could see the uniforms of police officers amongst them.

‘He’s dead,’ someone said.

‘Who—’ I tried to ask.

‘Seamus.’ Roland was standing at my side. ‘He’s been killed. Felled by a punch to the throat. They found him in the alley behind the old staircase.’

After that, we all had to give statements. We were corralled into the porter’s lodge by the sergeant, and one by one dictated what we knew to a young police officer. Indeed, we knew very little, apart from our witnessing the strange fight of the day before. Roland and I looked up as Professor Moriarty emerged. His expression was fixed, his eyes dark pools against the pallor of his face. He gave a brief nod in greeting, then headed back to his study.

At this point Eveline appeared, ready to give her statement. She seemed hesitant and nervous. I thought of the conversation I’d overheard, and wondered if she would tell the police about it.

Eventually, I escaped and went to meet Angela, luckily only a few minutes late, and my excuse was so dramatic and interesting that she forgave me instantly. We passed a pleasant evening, with a bowl of soup for supper and a walk in the warm twilight. She told me that she’d met her father for tea that day, as he had business in town. ‘We met someone who knew your professor,’ she said. ‘A friend of my father’s, a retired doctor. They were in the same tennis club once and they’ve kept in touch.’ But I was only half listening, distracted by the charm of the City at dusk, and the disturbing events of the day.

The next day a strange calm had descended upon the college. The police were a quiet presence in the common room. ‘There was a brawl,’ the young sergeant said, when Roland and I had gathered for a morning cup of tea. ‘It concerns a man named Edmund Sweeney, an Irishman, who was apparently known to the deceased.’

We agreed we had seen the fight, but we knew nothing of this Mr Sweeney. I assumed that Eveline must have told them.

‘Fenians.’ Dr McCrae spoke up. ‘London is awash with them.’

‘The Rebellion,’ someone said. ‘Thank God for our Army.’

‘And it’s not over,’ Dr McCrae said. ‘I reckon there’ll be war in Ireland by the end of the year.’

‘Fellow feeling, perhaps, Dr McCrae?’ It was Moriarty who spoke. He had appeared in the doorway, and now helped himself to a cup of tea from the urn.

‘Not at all, Professor. Not at all. No love lost between the Scots and the Irish.’

‘At least these Fenians have had the good sense to have a mathematician at their helm.’ Moriarty stirred sugar into his tea.

‘You mean Eamon de Valera.’ Dr McCrae raised a bushy eyebrow.

‘Indeed. Rockwell College Tipperary. Isn’t that so, Dr Brennan?’ Moriarty turned to Eveline.

She flashed him a look. Then she shrugged. ‘I’m afraid I wouldn’t know, Professor.’

‘The fallen angel,’ Moriarty said, amused. ‘One always needs one’s Lucifer.’ He turned on his heel and left, his cup and saucer balanced on one hand.

I spent an hour or two in my room, working on Cartesian coordinate systems for describing three-dimensional space. ‘Show your workings,’ Moriarty would always say, and I was trying to make sure that I’d written everything down, that it all made sense. But the figures swam before my eyes, distracted as I was by these terrible events in the college, and in the end I gave up and went for a walk.

I passed the porter’s lodge, now occupied by a new chap, a war veteran with blinking blue eyes and a shock of white hair. He sat uneasily in Seamus’s place, nodding silent greetings to those who came and went. As I started down the lane that led out to the back of the college, I heard raised voices.

‘You must get away.’ It was a woman’s tone.

‘I came here for you. I won’t leave without you,’ a rough, male voice replied and, as I rounded the corner, I could glimpse Dr Brennan and the man from the brawl, half hidden by the kitchen dustbins.

‘You’re risking your life,’ she said.

‘I’d risk anything for you, Bren. You know that.’

‘I thought you were dead. That night by the barricades, when they dragged you away … and now all this time later you appear in my life …’ She took a step towards him, and he enclosed her in his arms.

After a moment, she said, ‘But, our porter—’

‘Seamus O’Connor.’

‘I’d heard of him,’ she said. ‘He went over to the others—’

‘So he did. And, when he was interned, he held me responsible. Swore vengeance ever since.’

‘So, when you came in here—’

‘He set about me. Took me by surprise. Luckily I know how to defend myself.’

‘Oh, Edmund.’ She put her arms around him. ‘But, you’re not safe.’ Her eyes searched his face. ‘They’ll arrest you for his murder. You must go.’

‘But I didn’t do it, Bren. I swear to you. You know, on Monday, after picking that fight, he came to find me. Invited me for a drink. Took me down to the river for a pint of cockles and a glass of stout. The Old Red Lion, where your Starry Plough boys always used to drink. I thought it odd, but I didn’t want trouble.’

They stood a while, her head on his shoulder. After a moment, he smiled at her. ‘So, is this your life, then? Sitting up there doing your sums?’

‘It’s what I’ve always wanted,’ she said.

‘You were always one to get what you wanted,’ he said. ‘Tougher in battle than any man.’

‘Don’t be hard on me, Edmund,’ she said. ‘We’ve all suffered. We’ve all seen comrades shot dead before our eyes. You can’t blame me for wanting peace.’

‘Then come with me, Bren,’ he said. ‘Come back to the farm. I’ve been running too long.’

She shook her head, staring at the ground.

‘You should have been a wife, a mother—’

‘Not now.’ She faced him, her fingers soft against his collar. ‘If not with you, then with no one.’

He took a step back from her, stumbled a little. His hand went to his eyes.

‘Edmund? Are you all right?’

‘I’ll be fine.’

‘You’re ailing – you look dreadful.’

‘I’m fine.’

Another embrace, then she said, ‘I had no idea. I had no idea that our college porter was the self-same O’Connor who swore vengeance on you.’

A brief laugh. ‘We Irish. We get everywhere.’

‘Edmund – you must go. They’ll arrest you.’

He shook his head. ‘Whoever killed Seamus O’Connor, it was sure enough not me. Even though the world is a safer place without him.’

‘No one will believe you, Edmund.’

‘People saw us drinking together—’

‘From what I’ve heard of that man, he’d pour you a drink with one hand and poison it with the other.’

He gave a weary smile, took her in his arms.

‘It can’t be, Edmund.’ She broke away from him. ‘We both know that.’

He took her hand. ‘One more day. One more day together. And then I’ll leave you to your numbers.’

He put his arm around her, and they walked away, out of the college towards the square, where the white blossom of the trees dazzled in the sunlight.

I stood, wondering about what I’d seen, what I’d heard. I walked back slowly, into the college, hearing the bell strike the hour, aware that I was due at Moriarty’s rooms.

I found him standing, gazing at the wall, at his own portrait. He turned to me as I came into the room.

‘Mr Gifford – what is the matter?’

I explained that I’d just seen our main suspect in conversation with Dr Brennan, and that they’d left together. ‘Should we tell the police, Professor?’ I asked him.

He smiled. ‘I think we should get on with our work, Mr Gifford. The police have their methods, after all.’

That afternoon Angela finished her work early, so she came to find me at Moriarty’s rooms. I introduced them, and she greeted him with her shy charm. He shook her hand with formal politeness.

‘My friend here knows someone you know,’ I said.

‘Oh, hardly,’ she said. ‘My father knows him. We went to Baker Street, called at his rooms.’

The words had a peculiar effect. ‘Baker Street?’ Moriarty was staring at her intently. ‘Who? Who was it?’

‘My father’s friend was a doctor—’

‘But Holmes? Did you see Holmes?’

‘I think that was the man, yes.’

‘You met him? You met Sherlock Holmes? And what did he say?’

‘We hardly spoke, sir. It was only because my father was talking to Dr Watson, at the doorway there—’

‘But Holmes? Did he mention me? Moriarty?’ He waited breathlessly for her reply.

Angela answered timidly. ‘I had in passing told my father that Mr Gifford here was a member of this college. Dr Watson turned to his friend, and said, “Did you hear that, Holmes?” I think that’s what he said. Really, I wasn’t paying much attention, my father and Dr Watson were comparing notes on the Maida Vale Tennis club …’

‘Still there.’ Moriarty shook his head. ‘Still there. After all these years.’ He looked up again. ‘Reptilian, that’s how he describes me.’ His voice was harsh. ‘Did he say that? Mr Holmes?’

Angela appeared flustered. ‘Really, Professor, I had no reason to—’

‘Peering and blinking … Weaving my head from side to side, did he say that? Oh, and the rounded shoulders.’ He straightened himself. ‘What do you think?’

He was addressing me directly, standing stiff-necked and upright.

I didn’t know what to say. ‘Really, Professor, Miss Blunt hardly saw this man—’

‘I hold Dr Watson partly responsible. His account of things, he over-eggs it all in my view. A drama of equals, both of us brilliant, one good, one evil. Of course, real life is never like that. And, as for this tussle on the edge of the cliff that was supposed to carry me off … Watson should have known that I would never have engaged in hand-to-hand combat in that way. The truth is, we were just men. Flawed, as men are.’ The rage seemed to have left him, and he sank wearily into his chair. ‘Mr Holmes was very clever, of course, and captured something of the imagination of his time. But we’ve had a war since then. We’re tired. The jubilant escapades of Empire, it all seemed a game. But not now. We’ve seen a generation lost in pointless battle, the boundaries of Europe redrawn.’ He looked grey, and somehow flattened. His gaze went to Angela. ‘How is he, Mr Holmes? Does he seem tired too?’

‘I don’t really know.’ Angela glanced at me. ‘I hardly saw him. He was standing in the shadows, trying to light a pipe.’ She tugged at my sleeve.

‘We really must be going,’ I interjected. ‘Thank you for your help today. I’m returning you those Göttingen papers on the Kepler equation.’

‘Ah. Yes. Thank you.’ He didn’t look up, but gazed towards the window, a faraway look in his eyes.

‘Baker Street,’ he murmured to himself, as we left the room. ‘Baker Street,’ we heard him say.

The next morning was a Thursday, and I had hurried into the college in the hope of catching a few words with Professor Moriarty before I embarked on my teaching for the day. But there was no sign of him. I was standing outside his locked door, when a man approached along the corridor. ‘Ah,’ he said. ‘Not in yet?’

He was short and stocky, with a lined face, blue eyes and stilldark hair. ‘Come all this way to see him and he’s not even there.’ He flashed me a warm smile. ‘I’m Jack. I’m his brother.’

I took the proffered hand. ‘Pleased to meet you, sir,’ I said.

‘Well, when I say Jack – we have a joke we’re all called James. All three of us. So I had to choose another name.’

We stood in comfortable silence. The sunlight flickered along the wood panels of the corridor.

‘Not the sort to be late,’ Jack Moriarty said.

‘No,’ I agreed.

‘Can’t be late in my job.’ He smiled. ‘Them trains don’t wait for no one.’ He tapped his foot against the floor. ‘I’ll be back home tomorrow. Thank goodness.’

There was another silence.

‘I think these events have disturbed him rather,’ I said.

‘Oh, ah.’ He nodded. ‘I’d heard. He always spoke well of that porter. I think he got him that job in the first place. He has his networks. Anything you need, he’ll find it for you. A hunting rifle. A particularly fine tea. A rare medicinal remedy …’

Again, he retreated into silence. Around us, the sounds of the college – footsteps along corridors, a snatch of conversation, the wheeling of the kitchen trolleys from the refectory below.

Jack Moriarty spoke again. ‘Takes a lot to disturb my brother, mind you. The things that man has seen, and all you get is that blank smile.’ He was still tapping his foot, gazing down at the polished parquet. ‘I suppose I was the lucky one,’ he went on. ‘Being the youngest. After our mother died …’

This time the silence was awkward. ‘I’m sorry to hear that,’ I said.

He spoke slowly. ‘Jim joined the Army as soon as he could. Oldest brother, see, I always thought it was like family for a boy who’d never had a family. But James here …’ He looked up at me, his blue eyes clouded. ‘How can a man love, who’s never known love? That’s what I wonder.’

He said nothing more. After a moment I spoke again. ‘You had no parents?’

He sighed. ‘I was only a baby when she died. I was given away. Kindly couple, childless, showered me with affection. But James here was left with our father. And, let’s just say, he didn’t manage things very well. One day, he upped and left. Never saw him again. James came home from school as usual, he must have been about six or seven, a shy, quiet boy … and the house was locked up. Empty. His home, taken from under him. I heard later he was found, hours later, just standing there in the street, freezing cold, staring at the darkened windows.’

We were silent, thinking our own thoughts. Then, the sound of steps striding along the corridor.

‘Heavens, is that the time?’ Moriarty’s voice rang out. ‘I became entangled in a Manichean puzzle,’ he said. ‘I had no idea how late it had got.’ He greeted us with his characteristic smile. ‘You heard about our troubles here?’ he asked his brother, as we followed him into his rooms.

‘I had heard, yes. That poor porter of yours …’

Moriarty gestured for us both to sit down. ‘They’re hunting for his killer, I gather. An Irishman. Always the Irish, eh, Jack?’ He threw his brother a cheery smile.

‘Don’t we count as Irish, then?’ Jack sat down stiffly next to Moriarty’s desk.

‘A long time ago, perhaps. A long time ago. Now, where do you need me to sign?’

Jack opened one of the files and pulled out a document, cream foolscap tied with tape. ‘I hope this settles it once and for all,’ he said to his brother.

‘Oh, I’m sure it will,’ Moriarty said. ‘I know you have our best interests at heart.’

‘Jim has written to me. He’s in Afghanistan, apparently.’

‘Good luck to him. Those Pathans are nearly as bad as the Fenians.’ Moriarty laughed, and I wondered at his restored good humour.

‘Jim has affirmed that he supports our claim to the legacy.’

‘Good. Good.’ Moriarty nodded. He had taken a pen and now signed his name with a flourish. ‘And now, if you don’t mind, I must get on.’

Jack and I found ourselves outside his rooms once more, the door firmly shut.

‘A man of few words,’ Jack said. ‘He’s always preferred numbers.’

‘He seemed grateful to you. In his way.’ We began to walk together along the corridor.

Jack gave a nod. ‘What it is, see, is that our mother’s family owned some land, in Galway. Her brother allowed it to slip from his grasp, and now we’ve got the chance to get it back. It’s not for me, but I have a daughter, a sweet girl, newly married. I’d like her to have the proceeds. And James there, he’s always been keen to see justice done. In his own way. Mind you,’ he added, as we reached the main entrance, ‘it’s not solved yet. We’re in dispute with the son of the former owners, who’s determined to keep it at all costs. And now he’s disappeared. Only the odd threatening letter to show us he’s still in the fight. Well …’ He turned to me. ‘It was nice to meet you. I’m glad there’s someone in James’s life who can make him feel …’ Again, his gaze went to his feet, to the golden stone of the old steps. ‘He’s not an easy man, as I’m sure you know. He don’t need the money neither. No …’ He offered me his hand. ‘It’s about righting a wrong, all this. That’s the only thing that matters to him.’ We shook hands, and then he turned and walked out into the quad towards the porter’s lodge. I watched him go, thinking that whether he knew it or not, my professor was lucky to have such a brother.

That afternoon I went to find Roland in the common room for our customary cup of tea. The quad was peaceful, and I wondered about this trio that had somehow come to be here, this angry murderous man who had come here to find Eveline, only to risk his life with our quiet porter who seemed to want revenge. We were just pouring our tea when—

‘What the hell’s that?’ Dr McCrae ran to the window, as a terrible wail came from below.

In the middle of the quad stood the figure of Dr Brennan, motionless in her long skirt, her blouse pure white against the clipped green grass, her brown hair pinned up on top of her head.

Her hand was across her mouth, and she was making an extraordinary noise of pure distress.

‘He’s dead,’ she began to wail. ‘Poisoned.’

Again we raced downstairs. She was standing, stock still, repeating the cry, the word, ‘Poisoned.’

It was then that we saw him, Edmund Sweeney, lying on the steps by the porter’s lodge. He lay in an unnatural pose, his body twisted, his eyes wide open, his mouth a grimace of horror.

‘So trusting,’ she was saying. ‘A pint of stout down by the river. That’s all it took.’ She was shaking, crying, and Roland went to her and led her to a seat next to the lodge.

‘I was too late,’ she was murmuring. ‘I was too late.’

Someone had called the police, and now they arrived too, and a doctor, all of them examining the body of Edmund Sweeney.

‘I was too late,’ Eveline said again, louder now. ‘The betrayal of Seamus O’Connor,’ she went on, ‘to pretend to make up with him, while slipping something into his drink … And after all I’d done to make sure that the man I loved was safe. I caught Seamus alone, off his guard, just behind the lodge here. One move, and he was down. And I thought, the man I love will live.’

Her words hung in the air. The gathered crowd quietened, all eyes upon her.

She was calm now, and looked up at us all with a strange, empty smile. ‘Oh, I have nothing to lose. A punch to the throat,’ she said. ‘A ju-jitsu move, it’s lethal if done well.’

The crowd appeared to slow, to freeze. We stared at Dr Brennan, and she gazed back. ‘I killed Seamus to protect Edmund. But I was too late.’ Her words rang out in the silence.

The police officer took a step towards her. ‘Madam … am I right in understanding what you say? That … you … that the porter here … ?’

Again, the thin smile. ‘I had it all worked out. His enemy would be dead, he would be safe in Ireland, and I would take refuge in my calculations.’

She raised her hands to the policeman, who, red-faced and clumsy, locked his handcuffs around her wrists and led her awkwardly away.

We drifted back to the department in ones and twos, fragments of conversation along the corridor. ‘Always the worry with these Irish …’ ‘Never should have hired a woman …’

That night I slept fitfully. I arrived in college next morning hoping to find some solace in parabolic differentials. Moriarty’s door was locked. As the morning went on, there was still no sign of him. The department was abuzz with gossip and police. The body had shown signs of arsenic poisoning, someone said. ‘A slow death,’ someone else replied. ‘Two days. Most unpleasant.’

Later that day, Roland and I were together in my room when Jack Moriarty appeared at the door. He was out of breath and seemed upset. ‘No sign of him,’ he was saying. ‘I’ve got a spare key from the lodge.’

Roland and I hurried with him to Professor Moriarty’s room.

The room was bare. All books gone. Just the desk, two chairs, the empty shelves.

On the desk lay the Greuze painting, and next to it the Göttingen papers. They were labelled: ‘For Mr Gifford’.

We gazed around the empty space.

‘Gone,’ Jack said, at last.

‘How strange.’ It was Roland who spoke. ‘How odd to bail out like that. I know some of the chaps were a bit harsh on him. But I always liked him. You know, the other day, the day after poor Seamus was killed by our unreliable Dr Brennan, that other man was looking for her, skulking about downstairs, the police after him. And Professor Moriarty brought him in here, calmed him down, gave him a drink, sent him on his way. Didn’t give him away to the police at all.’ He pulled out his watch. ‘Well, students await. Toodle-pip.’ The door closed behind him.

Jack was staring at the painting. ‘You know,’ he said, his eyes fixed on the image of the boy, ‘I heard this morning, our claim to the farm has been settled. The one descendant left who was opposing our claim was found dead, yesterday. In this college.’

I touched the Göttingen papers, tracing my finger along the pages. ‘Kepler’s equation,’ I said. ‘Relating to the Two-Body problem.’

Our thoughts seemed to whisper in the silence. ‘Mathematics,’ Jack said, after a moment. ‘It asks for nothing back.’ He surveyed the empty room. ‘It’s always like this. He comes, he goes. Sometimes here, sometimes there. I’ll tie up this Galway land now that poor Mr Sweeney is out of the way. My brother’s share will be paid into his bank account.’ He turned towards the door. ‘I’m sure I’ll see him again when he deems it necessary.’

I picked up the painting under one arm, the papers under the other.

In the corridor, we shook hands. ‘Well,’ Jack said, ‘I don’t suppose I’ll see you again.’ He sighed. ‘Back home, see. A place of safety. A warm fire. My wife at my side.’ He shook my hand again, and we parted.

I walked out into the London afternoon. I thought about the two killings. Edmund Sweeney was the one man standing in the way of Moriarty’s inheritance. Seamus the porter had sworn to kill Edmund. And Moriarty, having made sure Seamus was installed in his porter’s lodge, then championed Eveline’s appointment. Knowing, all the while, that Edmund would find her, would follow her to the ends of the earth, thereby placing himself in the vicinity of Seamus – who wanted him dead.

A simple calculation.

But he hadn’t factored in one important thing: that Eveline loved Edmund so much that she would kill Seamus before Seamus could kill Edmund.

He hadn’t prepared for the workings of the human heart.

One thing I knew, from my father’s work: that arsenic would kill someone in half a day, not three. Whatever was making Edmund look so green on Wednesday, was probably nothing more than the cockles in the Old Red Lion.

And now, a year later, I am sitting in our little house in Greenwich. That autumn, Angela did me the honour of becoming my wife. We’re expecting our first child at the end of this year. Her father found me a rather good position as a clerk in a law firm, and it seemed only right that I should provide for my family. I catch myself thinking about Moriarty from time to time. The Greuze boy is on the wall of my study here. I look at his angelic blond curls and wonder if he, too, finds the glory of the heavens in the pure abstract truths of mathematics.

As for my work on the orbits of celestial bodies – one of these days I shall write it up. I shall give Professor Moriarty an acknowledgement. And, who knows, perhaps one day he’ll read it. Wherever he is.

The author would like to acknowledge Carl Murray, Professor of Mathematics and Astronomy at Queen Mary, for his scientific advice.