Enigma

1

THE WARTIME LIPSTICK was hard and waxy – it was like trying to colour your lips with a Christmas candle. When, after several minutes of hard rubbing, Hester Wallace replaced her glasses, she peered into the mirror with distaste. Make-up had never featured much in her life, not even before the war, when there had been plenty in the shops. But now, when there was nothing to be had, the lengths one was expected to go to were quite absurd. She knew of girls in the hut who made lipstick out of beetroot and sealed it in place with Vaseline, who used shoe polish and burnt cork for mascara and margarine wrappers as a skin softener, who dusted bicarbonate of soda into their armpits to disguise their sweat… She formed her lips into a cupid's bow, which she immediately drew back into a grimace. Really, it was quite, quite absurd.

The shortage of cosmetics seemed to have caught up at last even with Claire. Although there was a profusion of pots and bottles all over her little dressing table -Max Factor, Coty, Elizabeth Arden: each name redolent of pre-war glamour – most of them turned out on closer inspection to be empty. Nothing was left except a trace of scent. Hester sniffed at each in turn and her mind was filled with images of luxury- of satin cocktail dresses by Worth of London and gowns with daring decolletage, of fireworks at Versailles and the Duchess of Westminster's summer ball, and a dozen other wonderful nonsenses that Claire had prattled on about. Eventually she found a half-full pot of mascara and a glass-stoppered jar with an inch of rather lumpy face powder and set to work with those.

She had no qualms about helping herself. Hadn't Claire always told her she should? Making-up was fun, that was Claire's philosophy, it made one feel good about oneself, it turned one into someone else, and, besides, 'if this is what it takes, then, darling heart, this is simply what one does. Very well. Hester dabbed grimly at her pallid cheeks. If this was what it bloody well took to help persuade Miles Mermagen to approve a transfer, this was what he'd bloody well get.

She regarded her reflection without enthusiasm, then carefully replaced everything in its proper place and went downstairs. The sitting room was freshly swept. Daffodils above the hearth. A fire laid. The kitchen, too, was spotless. She had made a carrot flan earlier in the evening, enough for two, with ingredients she had grown herself in the little vegetable patch outside the kitchen door, and now she laid a place for Claire, and left a note telling her where to find the flan and instructions on how to heat it. She hesitated, then added at the end: 'Welcome back – from wherever you've been! – much love, H.' She hoped it didn't sound too fussy and inquisitive; she hoped she wasn't turning into her mother.

'ADU, Miss Wallace…'

Of course Claire would come back. It was all a stupid panic, too absurd for words.

She sat in one of the armchairs and waited for her until a quarter to midnight, when she dared leave it no longer.

As her bicycle bounced along the track towards the lane she startled a white owl which rose silently like a ghost in the moonlight.

In a way it was all Miss Smallbone's fault. If Angela Smallbone hadn't pointed out in the common room after prep that the Daily Telegraph was holding a crossword competition, then Hester Wallace's life would have gone on undisturbed. It was not a particularly thrilling life – a placid, provincial life in a remote and eccentric girls' preparatory school near the Dorset town of Beaminster, less than ten miles from where Hester had grown up. And it was not a life much touched by war, either, save for the pale faces of the evacuee children on some of the nearby farms, the barbed wire along the beach near Lyme Regis, and the chronic shortage of teaching staff- a shortage which meant that when the Michaelmas term began in the autumn of 1942, Hester was having to take divinity (her usual subject) and English and some Latin and Greek.

Hester had a gift for crosswords and when Angela read out that night that the prize-money was twenty pounds… well, she thought, why not? The first hurdle, an abnormally difficult puzzle printed in the next day's paper, she passed with ease. She sent off her solution and a letter arrived almost by return of post inviting her to the final, to be held in the Telegraph's staff canteen, a fortnight hence, a Saturday. Angela agreed to take over hockey practice, Hester caught the train from Crewkerne up to London, joined fifty other finalists – and won. She completed the crossword in three minutes and twenty-two seconds and Lord Camrose himself presented her with the cheque. She gave five pounds to her father for his church restoration fund, she spent seven pounds on a new winter coat (second-hand, actually, but good as new), and the rest she put in her Post Office savings account.

It was on the Thursday that the second letter had arrived, this one very different. Registered post, long buff envelope. On His Majesty's Service.

Afterwards, she could never quite decide. Had the Telegraph held the competition at the instigation of the War Office, as a way of trawling the country for men and women with an aptitude for word puzzles? Or had some bright spark at the War Office merely seen the results of the competition and asked the Telegraph for a list of the finalists? Whatever the truth, five of the most suitable were summoned to be interviewed in a grim Victorian office block on the wrong side of the Thames, and three of them were ordered to report to Bletchley.

The school hadn't wanted her to go. Her mother had cried. Her father had detested the idea, just as he detested all change, and for days beforehand he was filled with foreboding ('He shall return no more to his house, neither shall his place know him any more' Job 7.x). But the law was the law. She had to go. Besides, she thought, she was twenty-eight. Was she doomed to live out the rest of her life in the same place, tucked away in this drowsy quilt of tiny fields and honey-stoned villages? Here was her chance of escape. She had picked up enough clues at the interview to guess that the work would be codes, and her fantasies were all of quiet, book-lined libraries and the pure, clear air of the intellect.

Arriving at Bletchley station in her second-hand coat on a soaking Monday morning, she was taken straight by shooting brake to the mansion and given a copy of the Official Secrets Act to sign. The Army Captain who inducted them laid his pistol on the desk and said that if any of them, ever, breathed a word of what they were about to be told, he'd use it on them. Personally. Then they were assigned. The two male finalists became cryptanalysts, while she, the woman who had beaten them, was dispatched to a bedlam called Control.

'You take this form here, see, and in this first column you enter the code name of the intercept station. Chicksands, right, that's CKS, Beaumanor is BMR, Harpendon is HPN – don't worry, dear, you'll soon get used to it. Now here, see, you put the time of interception, here frequency, here call sign, here number of letter groups

Her fantasies were dust. She was a glorified clerk, Control a glorified funnel between the intercept stations and the cryptanalysts, a funnel down which poured the ceaseless output of some forty thousand different radio call signs, using more than sixty separately identified Enigma keys.

'German Air Force, right, they're usually either insects or flowers. So you've got Cockroach, say, that's the Enigma key for western fighters, based in France. Dragonfly is Luftwaffe in Tunis. Locust is Luftwaffe, Sicily. You've got a dozen of those. Your flowers are the Luftgau – Foxglove: eastern front, Daffodil: western front, Narcissus: Norway. Birds are for the German Army. Chaffinch and Phoenix, they're Panzerarmee Afrika. Kestrel and Vulture – Russian front. Sixteen little birdies. Then there's Garlic, Onion, Celery – all the vegetables are weather Enigmas. They go straight to Hut 10. Got it?'

'What are Skunk and Porcupine?'

'Skunk is Fliegerkorps VIII, eastern front. Porcupine is ground-air cooperation, southern Russia.'

'Why aren't they insects as well?'

'God knows.'

The charts they had to fill in were called either 'blists' or 'hankies', the filing cabinet for miscellaneous trivia was known as Titicaca ('an Andes lake fed by many rivers,' said Mermagen portentously, 'but with no outflow'). The men gave one another silly names -'the Unicorn-Zebra', 'the Mock Turtle' – while the girls mooned after the handsomer cryptanalysts in the Machine Room. Sitting in the freezing hut that winter, compiling her endless lists, Hester had a sense of Nazi Germany only as an endless, darkened plain, with thousands of tiny, isolated lights, flickering at one another in the blackness. Oddly enough, she thought, it was all, in its way, as remote from the war as the meadows and thatched barns of Dorset.

She parked her bicycle in the shed beside the canteen and was borne along by the stream of workers to be deposited near the entrance to Hut 6. Control was already in a fine state of uproar, Mermagen bustling self-importantly between the desks, knocking his head against the low-hanging lampshades, sending pools of yellow light spilling crazily in all directions. Fourth Panzer Army was reporting the successful recapture of Kharkov from the Russians and the ninnies in Hut 3 were demanding that every frequency in the southern sector, eastern front, be double-backed immediately.

'Hester, Hester, just in time. Will you talk to Chicksands, there's a good girl, and see what they can do? And while you're on, the Machine Room reckon they've got a corrupt text on the last batch of Kestrel -the operator needs to check her notes and re-send. Then the eleven o'clock from Beaumanor all need blisting. Grab someone to help you. Oh, and the Index could do with a sorting out.'

All this before she had even taken off her coat.

It was two o'clock before there was enough of a lull for her to get away and talk to Mermagen in private. He was in his broom-cupboard office, his feet up on the desk, studying a handful of papers through half-closed eyes, in a terrific man-of-destiny pose she guessed he'd copied from some actor in the pictures.

'I wondered if I might have a word, Miles.'

Miles. She found this insistence on first-name terms a tiresome affectation, but informality was a rigid rule, an essential part of the Bletchley ethos: we, the civilian amateurs shall defeat them, the disciplined Hun.

Mermagen continued to study his papers.

She tapped her foot. 'Miles?'

He flicked over a page. 'You have my completely divided attention.'

'My request for a transfer -'

He groaned and turned over another page. 'Not that again.'

'I've been learning German -'

'How brave.'

'You did say that not having German made a transfer impossible.'

'Yes, but I didn't say that having it made a transfer likely. Oh, bloody hell! Well, come in, then.'

With a sigh he put aside his papers and beckoned her over the threshold. Someone must have told him once that Brylcreem made him look racy. His oily black hair, swept back off his forehead and behind his ears, glistened like a swimmer's cap. He was trying to grow a Clark Gable moustache but it was slightly too long on the left-hand side.

'Transfers of personnel from section to section are, as I've told you before, extremely rare. We do have security to consider.'

Security to consider, this must have been how he turned down loans before the war. Suddenly he was staring at her intently and she realised he had noticed the make-up. He couldn't have looked more startled if she'd painted herself with woad. His voice seemed to drop an octave.

'Look here, Hester, the last thing I want is to be difficult. What you need is a change of scene for a day or two.' He touched his moustache lightly and gave a faint smile of recognition, as if he were surprised to find it still in place. 'Why don't you go up and take a look round one of the intercept stations, get a feel for where you fit into the chain? I know,' he added, 'I could do with a refresher myself. We could go up together.'

'Together? Yes… Why not? And find a little pub somewhere we could stop off for lunch?'

'Excellent. Make a real break of it.'

'Possibly a pub with rooms, so we could stay overnight if it got late?'

He laughed nervously. 'I still couldn't guarantee a transfer, you know.'

'But it would help?'

'Your words.'

'Miles?'

'Mmmm?'

'I'd rather die.'

'Frigid little bitch.'

She filled the basin with cold water and splashed her face furiously. The icy water numbed her hands and stung her face. It trickled down inside the neck of her shirt and up the sleeves. She welcomed the shock and the discomfort. She deserved it as a punishment for her folly and delusion.

She pressed her flat stomach against the edge of the basin and stared myopically at the chalk-white face in the mirror.

Useless to complain, of course. It was her word against his. She would never be believed. And even if she was – so what? My dear, it was simply the way of the world. Miles could ram her up against Lake bloody Titicaca if he liked, and put his hand up her skirt, and they'd still never let her go: nobody, once they'd seen as much as she had, was ever allowed to leave.

She felt a pricking of self-pity in the corners of her eyes and immediately lowered her head back over the basin and drenched her face, scrubbing at her cheeks and mouth with a sliver of carbolic soap until the powder stained the water pink.

She wished she could talk to Claire.

'ADU, Miss Wallace…'

Behind her in the cubicle the toilet flushed. Hurriedly, she pulled the plug out of the basin and dried her face and hands.

Name of intercept station, time of interception, frequency, call sign, letter groups… Name of intercept station, time of interception, frequency, call sign, letter groups…

Hester's hand moved mechanically across the paper.

At four o'clock the first half of the night-shift began drifting off to the canteen.

'Coming, Hetty?'

'Too much to do, unfortunately. I'll catch you up.'

'Poor you!'

'Poor you and bloody Miles,' said Beryl McCann, who had been to bed with Mermagen, once, and wished to God she hadn't.

Hester bent her head lower over her desk and continued to write in her careful schoolmistress copperplate. She watched the other women putting on their coats and filing out, their shoes clumping on the wooden floor. Ah, but Claire had been so funny about them. It was one of the things Hester loved in her the most, the way she mimicked everyone: Anthea Leigh-Delamere, the huntswoman, who liked to come on shift in jodhpurs; Binnie with the waxy skin who wanted to be a Catholic nun; the girl from Solihull who held the telephone a foot away from her mouth because her mother had told her the receiver was full of germs… As far as Hester knew, Claire had never even met Miles Mermagen, yet she could impersonate him to perfection. The ghastliness of Bletchley had been their shared and private joke, their conspiracy against the bores.

The opening of the outside door let in a sudden blast of freezing air. Blists and hankies rustled and fluttered in the chill.

Bores. Boring. Claire's favourite words. The Park was boring. The war was boring. The town was terrifically boring. And the men were the biggest bores of all. The men – my God, what scent was it she gave off? – there were always two or three of them at least, hanging round her like tomcats on heat. And how she mocked them, on those precious evenings when she and Hester were alone together, sitting companionably by the fireside like an old married couple. She mocked their clumsy fumblings, their corny dialogue, their absurd self-importance. The only man she didn't mock, now Hester came to think of it, was the curious Mr Jericho, whom she had never even mentioned.

'ADU, Miss Wallace…'.

Now that she had made up her mind to do it – and hadn't she always known, secretly, that she was going to do it? – she was astonished at how calm she felt. It would only be the briefest of glances, she told herself, and where was the harm in that? She even had the perfect excuse to slip across to the Index, for hadn't the beastly Miles, in everybody's hearing, commanded her to ensure the volumes were all arranged in proper order?

She finished the blist and slotted it into the rack. She forced herself to wait a decent interval, pretending to check the others' work, and then moved as casually as she could towards the Index Room.

2

Jericho drew back the curtains to unveil another cold, clear morning. It was only his third day in the Commercial Guesthouse but already the view had acquired a weary familiarity. First came the long and narrow garden (concrete yard with washing line, vegetable patch, bomb shelter) which petered out after seventy yards into a wilderness of weeds and a tumbledown, rotted fence. Then there was a drop he couldn't see, like a ha-ha, and then a broad expanse of railway lines, a dozen or more, which led the eye, at last, to the centrepiece: a huge Victorian engine shed with LONDON MIDLAND amp; SCOTTISH RAILWAY in white letters just visible beneath the grime.

What a day in prospect: the sort of day one waded through with no aim higher than to reach the other end intact. He looked at his Waralarm. It was a quarter past seven. It would be dark in the North Atlantic for at least another four hours. By his reckoning there would be nothing for him to do until – at the earliest -midnight, British time, when the first elements of the convoy would begin to enter the U-boat danger zone. Nothing to do except sit around the hut and wait and brood.

There had been three occasions during the night when Jericho had made up his mind to seek out Wigram and make a full confession, on the last of which he had actually got as far as putting on his coat. But in the end the judgement was too fine a one to call. On the one hand, yes, it was his duty to tell Wigram all he knew. On the other, no, what he knew would make little practical difference to the task of finding her, so why betray her? The equations cancelled one another out. By dawn he had surrendered, gratefully, to the old inertia, the product of always seeing both sides of every question.

And it could all still be some ghastly mistake -couldn't it, just? Some prank gone badly wrong? Eleven hours had passed since his conversation with Wigram. They might have found her by now. More likely, she would have turned up, either at the cottage or the hut – wide-eyed and wondering, darlings, what on earth the fuss was all about.

He was on the point of turning away from the window when his eye was caught by a movement at the far end of the engine shed. Was it a large animal of some sort, or a big man crawling on all fours? He squinted through the sooty glass but the thing was too far away for him to make it out exactly, so he fetched his telescope from the bottom of the wardrobe. The window sash was stuck but a few heavy blows from the heel of his hand were enough to raise it six inches. He knelt and rested the telescope on the sill. At first he couldn't find anything to focus on amid the dizzying crisscross of tracks but then, suddenly, it was filling his eye – an Alsatian dog as big as a calf, sniffing under the wheels of a goods wagon. He shifted the telescope a fraction to his left and there was a policeman dressed in a greatcoat that came down below his knees. Two policemen, in fact, and a second dog, on a leash.

He watched the little group for several minutes as they searched the empty train. Then the two teams split up, one passing further up the tracks and the other moving out of sight towards the little railway cottages opposite. He snapped the telescope shut.

Four men and two dogs for the railway yard. Say, a couple more teams to cover the station platforms. How many in the town? Twenty? And in the surrounding countryside?

'Got a photo of her? Something recent?'

He tapped the telescope against his cheek.

They must be watching every port and railway station in the country.

What would they do if they caught her?

Hang her?

Come on, Jericho. He could practically hear his housemaster's voice at his elbow. Brace up, boy.

Get through it somehow.

Wash. Shave. Dress. Make a little bundle of dirty laundry and leave it on the bed for Mrs Armstrong, more in hope than expectation. Go downstairs. Endure attempts to make polite conversation. Listen to one of Bonnyman's interminable, off-colour stories. Be introduced to two of the other guests: Miss Quince, rather pretty, a teleprincess in the naval hut, and Noakes, once an expert on Middle High German court epics, now a cryptanalyst in the weather section, vaguely known since 1940: a surly creature, then and now. Avoid all further conversation. Chew toast as stale as cardboard. Drink tea as grey and watery as a February sky. Half-listen to the wireless news: 'Moscow Radio reports the Russian Third Army under General Vatutin is making a strong defence of Kharkov in the face of the renewed German offensive

At ten to eight Mrs Armstrong came in with the morning post. Nothing for Mr Bonnyman ('thank God for that,' said Bonnyman), two letters for Miss Jobey, a postcard for Miss Quince, a bill from Heffers bookshop for Mr Noakes and nothing at all for Mr Jericho – oh, except this, which she'd found when she came down and which must have been put through the door some time in the night.

He held it carefully. The envelope was poor-quality, official-issue stuff, his name printed on it in blue ink, with 'By hand, Strictly Personal' added underneath and double-underlined. The 'e' in Jericho and in 'Personal' was in the Greek form. His nocturnal correspondent was a classicist, perhaps?

He took it into the hall to open, Mrs Armstrong at his heels.

Hut 6

4.45 A.M.

Dear Mr Jericho,

As you expressed such a strong interest in medieval alabaster figurework when we met yesterday, I wondered if you might care to join me at the same place at 8 this morning to view the altar tomb of Lord Grey de Wilton (15th cent, and really very fine)?

Sincerely,

H.A.W.

'Bad news, Mr Jericho?' She couldn't quite suppress the note of hope in her voice.

But Jericho was already dragging on his overcoat and was halfway out of the door.

Even after taking the hill at a fast trot he was still five minutes late by the time he passed the granite war memorial. There was no sign of her or anyone else in the graveyard so he tried the door to the church. At first he thought it was locked. It took both hands to turn the rusty iron ring. He put his shoulder to the weathered oak and it shuddered inwards.

The church inside was cave-like, cold and dark, the shadows pierced by shafts of dusty, slate-blue light, so solid they seemed to have been propped like slabs against the windows. He hadn't been in a church for years and the chilly stink of candle wax and damp and incense brought memories of childhood crawling back. He thought he could make out the shape of a head in one of the pews nearest the altar and began to walk towards it.

'Miss Wallace?' His voice was hollow and seemed to travel a great distance. But when he came closer he saw it wasn't a head, just a priest's vestment, draped neatly over the back of the pew. He passed on up the nave to the wood-panelled altar. To the left was a stone coffin with an inscription; next to it, the smooth, white effigy of Richard, Lord Grey de Wilton, dead these past five hundred years, reclining in full armour, his head resting on his helmet, his feet on the back of a lion.

'The armour is especially interesting. But then warfare in the fifteenth century was the highest occupation for a gentleman.'

He wasn't sure where she'd come from. She was simply there when he turned round, about ten feet behind him.

'And the face, I think, is also good, if unexceptional. You weren't followed, I trust?'

'No. I don't think so, no.'

She took a few steps towards him. With her dead complexion and tapering white fingers she might have been an alabaster effigy herself, climbed down from Lord Grey's tomb.

'Perhaps you noticed the royal arms above the north door?'

'How long have you been here?'

'The arms of Queen Anne, but, intriguingly, still of the Stuart pattern. The arms of Scotland were only added as late as 1707. Now that is rare. About ten minutes. The police were just leaving as I arrived.' She held out her hand. 'May I have my note back, please?'

When he hesitated she presented her palm to him again, more emphatically this time.

The note, please, if you'd be so good. I'd prefer to leave no trace. Thank you.' She took it and stowed it away at the bottom of her voluminous carpet bag. Her hands were shaking so much she had trouble fastening the clasp. 'There's no need to whisper, by the way. We're quite alone. Apart from God. And He's supposed to be on our side.'

He knew it would be wise for him to wait, to let her come to it in her own time, but he couldn't help himself.

'You've checked it?' he said. 'The call sign?'

She finally snapped the bag shut. 'Yes. I've checked it.'

'And is it Army or Luftwaffe?'

She held up a finger. 'Patience, Mr Jericho. Patience. First there's some information I'd like from you, if you don't mind. We might begin with what made you choose those three letters.'

'You don't want to know, Miss Wallace. Believe me.'

She raised her eyes to heaven. 'God preserve me: another one.'

'I'm sorry?

'I seem to move in an endless round, Mr Jericho, from one patronising male to another, for ever being told what I am and am not allowed to know. Well, that ends here.' She pointed to the flagstone floor.

'Miss Wallace,' said Jericho, catching the same tone of cool formality, 'I came in answer to your note. I have no interest in alabaster figurework – medieval, Victorian or ancient Chinese, come to that. If you've nothing else to tell me, good morning to you.'

'Then good morning.'

'Good morning.'

If he'd had a hat he would have raised it.

He turned and began his progress down the aisle towards the door. You fool, said a voice at his inner ear, you bloody conceited fool. By the time he'd gone half way his pace had slowed and by the time he reached the font he stopped. His shoulders sagged.

'Checkmate, I believe, Mr Jericho,' she called cheerfully from beside the altar.

'ADU was the call sign on a series of four intercepts our… mutual friend… stole from Hut 3.' His voice was weary.

'How do you know she stole them?'

'They were hidden in her bedroom. Under the floorboards. As far as I know, we're not encouraged to take our work home.'

'Where are they now?'

'I burned them.'

They were sitting in the second row of pews, side by side, facing straight ahead. Anyone coming into the church would have thought it was a confession – she playing the priest and he the sinner.

'Do you think she's a spy?'

'I don't know. Her behaviour is suspicious, to put it charitably. Others seem to think she is.'

'Who?'

'A man from the Foreign Office called Wigram, for one.'

'Why?'

'Obviously because she's disappeared.'

'Oh, come. There must be more to it than that. All this fuss for one missed shift?'

He ran his hand nervously through his hair.

'There are… indications – and don't, for God's sake, ask me to tell you what they are – just indications, all right, that the Germans may suspect Enigma is being broken.'

A long pause.

'But why would our mutual friend wish to help the Germans?

'If I knew that, Miss Wallace, I wouldn't be sitting here with you, passing the time of day breaking the Official Secrets Act. Now, really, please, have you heard enough?'

Another pause. A reluctant nod of the head.

'Enough.'

She told it like story, in a low voice, without looking at him. She used her hands a lot, he noticed. She couldn't keep them still. They fluttered like tiny white birds -now pecking at the hem of her coat, pulling it demurely across her knees, now perching on the back of the pew in front, now describing, in rapid, circling motions, how she had gone about her crime.

She waits until the other girls have gone off on their meal break.

She leaves the door to the Index Room open a fraction, so as not to look suspicious and to ensure a good warning of anyone's approach.

She reaches up to the dusty metal shelf and drags down the first volume.

AAA, AAB, AAC…

She flicks through to the tenth page.

And there it is. The thirteenth entry.

ADU.

She runs her finger along the line to the row and column entries and notes their numbers on a scrap of paper.

She puts the index volume back. The row ledger is on a higher shelf and she has to fetch a stool to get it.

She stops off on her way to bob her head around the door and check the corridor.

Deserted.

Now she is nervous. Why? she asks herself. What is she doing that's so terribly wrong? She smooths her hands down over her grey skirt to dry her palms, then opens the book. She turns the pages. She finds the number. Again, she follows the line across.

She checks it once, and then a second time. There's no mistake.

ADU is the call sign of Nachrichten-Regimenter 537 – a motorised German Army signals unit. Its transmissions are on wavelengths monitored by the Beaumanor intercept station in Leicestershire. Direction-finding has established that, since October, Unit number 537 has been based in the Smolensk military district of the Ukraine, presently occupied by Wehrmacht Army Group Centre under the command of Field Marshal Gunther von Kluge.

Jericho had been leaning forwards in anticipation. Now he drew back in surprise. 'A signals unit?"

He felt obscurely disappointed. What exactly had he been expecting? He wasn't sure. Just something a little more… exotic, he supposed.

'537,' he said, 'is that a front-line unit?'

'The line in that sector is shifting every day. But according to the situation map in Hut 6, Smolensk is still about a hundred kilometres inside German territory.'

'Ah.'

'Yes. That was my reaction – at first, anyway. I mean, this is a standard, rear-echelon, low-priority target. This is workaday in the extreme. But there are several… complications.' She fished in her bag for a handkerchief and blew her nose. Again, Jericho observed the slight trembling of her fingers.

After replacing the row volume it is the work of less than a minute to pull down the appropriate column book and make a note of the intercept serial numbers. When she comes out of the Index Room, Miles ('that's Miles Mermagen,' she adds in parenthesis, 'Control Room duty officer: a bear of very little brain')

Miles is on the telephone, his back to the door, oiling up to someone in authority – 'No, no, that's absolutely fine, Donald, a pleasure to be of service…' – which suits Hester beautifully for it means he never even notices her collect her coat and leave. She clicks on her blackout torch and steps out into the night.

A gust of wind swirls down the alley between the huts and buffets her face. At the far end of Hut 8 the path forks: right will take her to the main gate and the warm bustle of the canteen, left leads into the blackness along the edge of the lake.

She turns left.

The moon is wrapped in a tissue of cloud but the pale light is just luminous enough to show her the way. Beyond the eastern perimeter fence lies a small wood which she can't see, but the sound of the wind moving through the invisible trees seems to pull her on. Past A-and B-Blocks, two hundred and fifty yards, and there it is, straight ahead, faintly outlined: the big, squat, bunkerlike building, only just completed, that now houses Bletchley's central Registry. As she comes closer her torch flashes on steel-shuttered windows, then finds the heavy door.

Thou shalt not steal, she tells herself, reaching for the handle.

No, no. Of course not.

Thou shalt not, steal, thou wilt merely take a quick look, and then depart.

And, in any case, don't 'the secret things belong unto the Lord our God' (Deuteronomy 29.xxix)?

The rawness of the white neon is a shock after the gloom of the hut, and so is the calm, ruffled only by the distant clatter of the Hollerith punch-card machines. The workmen still haven't finished. Brushes and tools are stacked to one side of a reception area that is thick with the smell of building work – fresh concrete, wet paint, wood-shavings. The duty clerk, a corporal in the Women's Auxiliary Air Force, leans across the counter in a friendly way as if she is serving in a shop.

'Cold night?'

'Rather.' Hester manages to smile and nod. 'I've got some serials to check.'

'Reference or loan?'

'Reference.'

'Section?'

'Hut 6 Control.'

'Pass?'

The woman takes the list of numbers and disappears into a back room. Through the open door Hester can see stacks of metal shelving, infinite rows of cardboard files. A man strolls past the doorway and takes down one of the boxes. He stares at her. She looks away. On the whitewashed wall is a poster, a Bateman cartoon showing a woman sneezing, accompanied by some typical, fatuous Whitehall busybodying:

THE MINISTRY OF HEALTH says:-

Coughs and sneezes spread diseases

Trap the germs by using your handkerchief

Help to keep the Nation Fighting Fit

There is nowhere to sit. Behind the counter is a large clock with 'RAF' stamped on its face – so large, in fact, that Hester can actually see the big hand moving. Four minutes pass. Five minutes. The Registry is unpleasantly hot. She can feel herself starting to sweat. The stench of paint is nauseating. Seven minutes. Eight minutes. She would like to flee, but the corporal has taken her identity card. Dear God, how could she have been so utterly stupid? What if the clerk is now on the phone to Hut 6, checking up on her? At any instant, Miles will come crashing into the Registry: 'What the hell d'you think you're doing, woman?' Nine minutes. Ten minutes. Try to focus on something else. Coughs and sneezes spread diseases…

She's in such a state, she actually fails to hear the clerk come up behind her.

'I'm sorry to have been so long, but I've never come across anything like this

The girl, poor thing, is rather shaken.

'Why?' asked Jericho.

'The file,' said Hester. 'The file I'd asked her for? It was empty.'

There was a loud metallic crack behind them and then a series of short scrapes as the church door was pushed open. Hester closed her eyes and dropped to her knees on one of the cassocks, tugging Jericho down beside her. She clasped her hands and lowered her head and he did the same. Footsteps came halfway up the aisle behind them, stopped, and then resumed slowly on tiptoe. Jericho glanced surreptitiously to his left in time to see the elderly priest bending to retrieve his vestment.

'Sorry to interrupt your prayers,' whispered the vicar. He gave Hester a little wave and a nod. 'Hello there. So sorry. I'll leave you to God.'

They listened to his fussy tread fading towards the back of the church. The door was tugged shut. The latch fell with a crash. Jericho sat back on the pew and laid his hand over his heart and swore he could feel it beating through four layers of clothing. He looked at Hester – I'll leave you to God?' he repeated – and she smiled. The change it wrought in her was remarkable. Her eyes shone, the hardness in her face softened – and for the first time he briefly glimpsed the reason why she and Claire might have been friends.

Jericho contemplated the stained-glass window above the altar and made a steeple of his fingers. 'So what exactly are we to make of this? That Claire must have stolen the entire contents of the file? No -' he contradicted himself immediately ' – no, that can't be right, can it, because what she had in her room were the original cryptograms, not the decodes…,?'

'Precisely,' said Hester. 'There was a typewritten slip in the Registry file which the clerk showed me – words to the effect that the enclosed serial numbers had been reclassified and withdrawn, and that all enquires should be addressed to the office of the Director-General.'

'The Director-General! Are you sure?'

'I can read, Mr Jericho.'

'What was the date on the slip?'

'March the 4th.'

Jericho massaged his forehead. It was the oddest thing he'd ever heard. 'What happened after the Registry?'

'I went back to the hut and wrote my note to you. Delivering that took the rest of my meal break. Then it was a matter of getting back into the Index Room whenever I could. We deep a daily log of all intercepts, made up from the blists. One file for each day.' Once again she rummaged in her bag and withdrew a small index-card with a list of dates and numbers. 'I wasn't sure where to start so I simply went right back to the beginning of the year and worked my way through. Nothing recorded till February the 6th. Only eleven interceptions altogether, four of which came on the final day.'

'Which was what?'

'March the 4th. The same day the file was removed from the Registry. What do you make of that?'

'Nothing. Everything. I'm still trying to imagine what a rear-echelon German signals unit could possibly say that would warrant the removal of its entire file.'

'The Director-General is who, as a matter of interest?'

'The chief of the Secret Intelligence Service. "C". I don't know his real name.' He remembered the man who had presented him with the cheque just before Christmas. A florid face and hairy country tweeds. He had looked more like a farmer than a spy master. 'Your notes,' he said, holding out his hand. 'May I?'

Reluctantly she handed him the list of interceptions. He held it towards the pale light. It certainly made a bizarre pattern. Following the initial interception, just after noon on 6 February, there had been two days of silence. Then there had been another signal at 1427 hours on the 9th. Then a gap of ten days. Then a broadcast at 1807 on the 20th, and another long gap, followed by a flurry of activity: two signals on 2 March (1639 and 1901), two on the 3rd (1118 and 1727), and finally four signals, in rapid succession, on the night of the 4th. These were the cryptograms he had taken from Claire's room. The broadcasts had begun just two days before his final conversation with Claire at the flooded clay pit. And they had ended a month later, while he was still at Cambridge, less than a week before the Shark blackout.

There was no shape to it at all.

He said: 'What Enigma key were they transmitted in? They were enciphered in Enigma, I take it?'

'In the Index they were catalogued as Vulture.'

'Vulture?'

'The standard Wehrmacht Enigma key for the Russian front.'

'Broken regularly?'

'Every day. As far as I know.'

'And the signals – how were they sent? They were, what, just carried on the usual military net?'

'I don't know, but I'd say almost certainly not.'

'Why?'

'There's not enough traffic, for a start. It's too irregular. And the frequency's not one I recognise. It feels to me like something rather more special – a private line, as it were. Just the two stations: a mother and a lone star. But we'd need to see the log sheets to be certain.'

'And where are they?'

'They should have been in the Registry. But when we checked we found they'd all been removed as well.'

'My, my,' murmured Jericho, 'they really have been thorough.'

'Short of tearing the sheets out of the Control Room Index, they couldn't have done much more. And you think she's behaving suspiciously? I'll have that back now, if I may.'

She took the record of the interceptions and bent forwards to hide it in her bag.

Jericho rested his head on the back of the pew and stared up at the vaulted ceiling. Special? he though. I'll say it was special, more than special for the Director-General himself to palm the entire bloody file, plus all the log sheets. There was no sense to it. He wished he weren't so damned tired. He needed to shut his study door for a day or two, sport his oak, find a good, fresh pile of clean notepaper and a set of sharpened pencils…

He slowly let his gaze descend to take in the rest of the church – the saints in their windows, the marble angels, the stone memorials to the respectable dead of Bletchley parish, the ropes from the belfry looped together like a hanging spider beneath the gloomy organ loft. He closed his eyes.

Claire, Claire, what have you done? Did you see something you weren't supposed to in that 'deadly dull' job of yours? Did you rescue a few scraps from the confidential waste when nobody was looking and spirit them home? And if you did that, why? And do they know you did it? Is that why Wigram's after you? Have you learned too much?

He saw her on her knees in the darkness at the foot of his bed, heard his own voice slurred with sleep -' What on earth are you doing?' – and her ingenuous reply: 'I'm just going through your things…'

You were always looking for something, weren't you? And when I couldn't provide it, you just went on to someone else. (' There's always someone else,' you said: almost the last words you ever spoke to me, remember?) What is it, then, this thing you want so badly?

So many questions. He realised he was beginning to freeze. He huddled down into his coat, burying his chin in his scarf, thrusting his hands deep into his pockets. He tried to recall the images of the four cryptograms – LCNNR KDEMS LWAZA – but the letters were blurred. He had found this before. It was impossible mentally to photograph pages of gibberish: there had to be some meaning to them, some structure, to fix them in his mind.

'A mother and a lone star…'

The thick walls held a silence that seemed as old as the church itself – an oppressive silence, interrupted only occasionally by the rustling of a bird nesting in the rafters. For several minutes neither of them spoke.

Sitting on the hard bench, Jericho felt as though his bones had turned to ice, and this numbness, combined with the silence and the reliquaries everywhere and the sickly smell of incense, made him morbid. His father's funeral came to him for the second time in two days – the gaunt face in the coffin, his mother forcing him to kiss it goodbye, the cold skin beneath his lips giving off a sour reek of chemicals, like the school lab, and then the even worse stench at the crematorium. 'I need some air,' he said.

She gathered her bag and followed him down the aisle. Outside they pretended to study the tombs. To the north of the churchyard, screened by trees, was Bletchley Park. A motorcycle passed noisily down the lane towards the town. Jericho waited until the crack of its engine had dwindled to a drone in the distance and then said, almost to himself: 'The question I keep asking myself is why did she steal cryptograms? I mean, given what else she could have taken. If one was a spy -' Hester opened her mouth to protest and he held up his hand. 'All right, I'm not saying that she is, but if one was, surely one would want to steal proof that Enigma was being broken? What earthly use is an intercept?' He lowered himself to his haunches and ran his fingers over an inscription that had almost crumbled away. 'If only we knew more about them… To whom they were sent, for instance.'

'We've been over this. They've removed every trace.' 'But someone must know something,' he mused. For a start, someone must have broken the traffic. And someone else must have translated it.'

'Why don't you ask one of your cryptanalyst friends? You're all terrifically good chaps together, aren't you?'

'Not especially. In any case I'm afraid we're encouraged to lead quite separate lives. There is a man in Hut 3 who might have seen them…' But then he remembered Weitzman's frightened face ('please don't ask me, I don't want to know…') and he shook his head. 'No. He wouldn't help.'

'Then what a pity it is,' she said, with some asperity, 'that you burned our only clues.'

'Keeping them was too much of a risk.' He was still rubbing slowly at the stone. 'For all I knew, you might have told Wigram I'd asked you about the call sign.' He looked up at her uneasily. 'You didn't, I take it?'

'Credit me with some sense, Mr Jericho. Would I be here talking to you now?' She stamped off down the row of graves and began furiously studying an epitaph.

She regretted her sharpness almost at once. ('He that is slow to anger is better than the mighty; and he that ruleth his spirit than he that taketh a city.' Proverbs 16.xxxii.) But then, as Jericho pointed out later, when relations between them had improved sufficiently for him to risk the observation, if she hadn't lost her temper, she might never have thought of the solution.

'Sometimes,' he said, 'we need a little tension to sharpen our wits.'

She was jealous, that was the truth of it. She had thought she knew Claire as well as anyone but it was fast becoming apparent that she knew her hardly at all, scarcely better even than he did.

She shivered. There was no warmth in this March sun. It fell on the stone tower of St Mary's as cold as light from a looking glass.

Jericho was back on his feet now, moving between the graves. She wondered whether she might have been like him if she'd been allowed to go to university. But her father wouldn't stand for it and her brother George had gone instead, as if it were God's law: men go to university, men break codes; women stay at home, women do the filing.

'Hester, Hester, just in time. Will you talk to Chicksands, there's a good girl, and see what they can do? And while you're on, the Machine Room reckon they've got a corrupt text on the last batch of Kestrel- the operator needs to check her notes and re-send. Then the eleven o 'clocks from Beaumanor…'

She had been standing slack with defeat, gazing at a tombstone, but now she felt her body slowly coming to attention.

'The operator needs to check her notes…'

'Mr Jericho!'

He turned at the sound of his name to see her stumbling through the graves towards him.

It was almost ten o'clock and Miles Mermagen was combing his hair in his office, preparatory to returning to his digs, when Hester Wallace appeared at his office door.

'No,' he said, with his back to her.

'Miles, listen, I've been thinking, you were right, I've been an utter fool.'

He squinted suspiciously at her in the mirror.

'My application for a transfer – I want you to withdraw it.'

'Fine. I never submitted it.'

He returned his attention to himself. The comb slid through the thick black hair like a rake through oil.

She forced a smile. 'I was thinking about what you said, about needing to know where one fits into the chain…' He finished his grooming and turned his profile to the mirror, trying to look at his reflection sideways on. 'If you remember, we talked about my possibly going to an intercept station.'

'No problem.'

'I thought, well, I'm not due on shift till tomorrow afternoon – I thought I might go today.'

'Today?' He looked at his watch. 'Actually, I'm tied up, rather.'

'I could go on my own, Miles. And report my finding -' behind her back she dug her nails into her palm '- one evening.'

He gave her another narrowed look and she thought, No, no, really this is too obvious, even for him, but then he shrugged. 'Why not? Better call them first.' He waved his hand grandly.

'Invoke my name.' 'Thank you, Miles.'

'Lot's wife, what?' He winked. 'Pillar of salt by day, ball of fire by night.,.?'

On the way out he patted her bottom.

Thirty yards away, in Hut 8, Jericho was knocking on the door marked us NAVY LIAISON. A loud voice told him to 'come on in'.

Kramer didn't have a desk – the room wasn't big enough – just a card table with a telephone on it and wire baskets filled with papers stacked on the floor. There wasn't even a window. On one of the wooden partitions separating him from the rest of the hut he'd taped a recent photograph, torn out of Life magazine, showing Roosevelt and Churchill at the Casablanca conference, sitting side by side in a sunny garden. He noticed Jericho staring at it.

'When you fellers get me really down I look at it and think – well, hell, if they can do it, so can I.' He grinned. 'Got something to show you.' He opened his attache case and pulled out a wad of papers marked MOST SECRET: ULTRA. 'Skynner finally got the order to give them me this morning. I'm supposed to get them off to Washington tonight.'

Jericho flicked through them. A mass of calculations that were half familiar, and some complex technical drawings of what looked like electronic circuitry.

Kramer said: 'The plans for the prototype four-wheel bombes.'

Jericho looked up in surprise. 'They're using valves?'

'Sure are. Gas-filled triode valves. GTIC thyatrons.'

'Good God.'

'They're calling it Cobra. The first three wheel-settings will be solved in the usual way on the existing bombes – that is, electro-mechanically. But the fourth – the fourth- will be solved purely electronically, using a relay rack and valves, linked to the bombe by this fat cable form, that looks like a -' Kramer cupped his hands into a circle '- well, that looks like a cobra, I guess. Using valves in sequence – that's a revolution. Never been done before. Your people say it should make the calculations a hundred times, maybe a thousand times, as fast.'

Jericho said, almost to himself: 'A Turing machine.'

'A what?'

'An electronic computer.'

'Well, whatever you want to call it. It works in theory, that's the good news. And from what they're saying, this may be just the start. It seems they're planning some kind of super-bombe, all electronic, called Colossus.'

Jericho had a sudden vision of Alan Turing, one winter afternoon, sitting cross-legged in his Cambridge study while the lamps came on outside, describing his dream of a universal calculating machine. How long ago had that been? Less than five years?

'And when will this happen?'

'That's the bad news. Even Cobra won't be operational till June.'

'But that's appalling.'

'Same old goddamn story. No components, no workshops, not enough technicians. Guess how many men are working on this thing right now, as we speak.'

'Not enough, I expect.'

Kramer held up one hand and spread his fingers close to Jericho's face. 'Five. Five!' He stuffed the papers back into his case and snapped the lock. 'Something's got to be done about this.' He was muttering and shaking his head. 'Got to get something moving.'

'You're going to London?'

'Right now. Embassy first. Then on across Grosvenor Square to see the admiral.'

Jericho winced with disappointment. 'I suppose you're taking your car?'

'Are you kidding. With this?' He patted the case. 'Skynner's making me go with an escort. Why?'

'I was just wondering – I know this is an awful cheek, but you said if I had a favour to ask – I was wondering if I might possibly borrow it?'

'Sure.' Kramer pulled on his overcoat. I'll probably be gone a couple of days. I'll show you where she's parked.' He collected his cap from the back of the door and they went out into the corridor.

By the entrance to the hut they ran into Wigram. Jericho was surprised at how unkempt he looked. He had obviously been up all night. A dusting of reddish-blond stubble glinted in the sunlight.

'Ah, the gallant lieutenant and the great cryptanalyst. I heard you two were friends.' He bowed with mock formality and said to Jericho: Til need to talk to you again later, old chap.'

'Now there's a guy who gives me the creeps,' said Kramer, as they walked up the path towards the mansion. 'Had him in my room for about twenty minutes this morning, asking me questions about some girl I know.'

Jericho almost trod on his own feet.

'You know Claire Romilly?'

'There she is,' said Kramer, and for an instant Jericho thought he meant Claire but actually he was pointing to his car. 'She's still warm. The tank's full and there's a can in the back.' He fished in his pocket for the key and threw it to Jericho. 'Sure I know Claire. Doesn't everybody? Hell of a girl.' He patted Jericho on the arm. 'Have a nice trip.'

3

It was another half-hour before Jericho was able to get away.

He climbed the concrete steps to the Operations Room where he found Cave sitting alone at the end of the long table, telephones on either side of him, staring up at the Atlantic Plot. Eleven Shark signals had been intercepted since midnight, he said, none of them from the anticipated battle zone, which was bad news. Convoy HX-229 was within 150 miles of the suspected U-boat lines, steaming directly due east, full tilt towards them, at a speed of 10.5 knots. SC-122 was slightly ahead of her, to the north east. HX-229A was well back, heading north up the coast of Newfoundland. 'Nearly light,' he said, 'but the weather's getting worse, poor sods.'

Jericho left him to it and went in search, first, of Logie, who dismissed him with a wave of his pipe ('Fine, old love, you rest up, curtain rises twenty hundred'), and then of Atwood, who eventually agreed to lend him his pre-war AA touring atlas of the British Isles. ('"Roll up that map,"' he quoted wistfully, as he produced it from beneath his desk, "'it will not be wanted these ten years.'")

After that he was ready.

He sat in the front seat of Kramer's car and ran his hands over the unfamiliar controls and it occurred to him that he'd never quite got round to learning how to drive. He knew the basic principles, of course, but it must have been six or seven years since his last attempt, and that had been in his stepfather's huge and tanklike Humber – a vastly different proposition to this little Austin. Still, at least he wasn't doing anything illegal: in a country where one nowadays practically needed a permit to visit the lavatory, it was for some reason no longer necessary to have a driving licence.

He took several minutes trying to sort out clutch pedal from accelerator, handbrake from gear lever, then pulled out the choke and switched on the ignition. The car rocked and stalled. He put the gears into neutral and tried again and this time, miraculously, as his left foot lifted off the clutch, the car crawled forwards.

At the main gate he was waved down and managed to bring the car gliding to a halt. One of the sentries opened his door and he had to climb out while another got in to search the interior.

Half a minute later the barrier was rising and he was through.

He drove at a cyclist's pace along the narrow lanes towards Shenley Brook End, and it was this low speed that saved him. The plan he had agreed with Hester Wallace – assuming he could get Kramer's car – was that he would pick her up from the cottage, and he was just rounding the bend a quarter of a mile before the turning when something flashed dark in the field up ahead on the right. Immediately, he swerved up on to the verge and braked. He left the engine running then cautiously opened the door and clambered out on the running board to get a better view.

Policemen again. One moving stealthily around the edge of the field. Another half hidden in the hedge, apparently watching the road outside the cottage.

Jericho dropped back into the driver's seat and tapped his fingers on the steering wheel. He wasn't sure whether he had been seen but the sooner he got out of their range of vision the better. The gear change was stiff and it took both hands to jam the lever into reverse. The engine clanked and whined. First he nearly backed into the ditch, then he overcorrected and the car went weaving drunkenly across the road, mounted the opposite bank and stalled. It was not an elegant piece of parking but at least he was sufficiently far back around the curve for the policemen to be out of sight.

They had to have heard him, surely? At any moment one of them would come strolling down the lane to investigate, and he tried to think up some excuse for his lunatic behaviour, but the minutes passed and nobody appeared. He switched off the ignition and the only sound was birdsong.

No wonder Wigram looked so tired, he thought. He appeared to have taken over command of half the police force of the county – probably of the country, for all Jericho knew.

Suddenly, the scale of the odds stacked against them struck him as so overwhelming, he was seriously tempted to jack in the whole damn fool project. ('We must go to the intercept station, Mr Jericho – go to Beaumanor and get hold of the operator's handwritten notes. They keep them for at least a month and they'll never have dreamed of removing those – I'll take a wager on it. Only we poor drones have anything to do with them.) Indeed, he might well have turned the car round that very minute and driven back to Bletchley if there hadn't been a loud tapping noise at the window to his left. He must have jumped a full inch in his seat.

It was Hester Wallace, although at first he didn't recognise her. She had exchanged her skirt and blouse for a heavy tweed jacket and a thick sweater. A pair of brown corduroy trousers were tucked into the tops of grey woollen socks, and her stout boots were so clogged with mud they seemed the size of a carthorse's hooves. She hefted her bulging carpetbag into the back of the Austin and sank down low in the passenger seat. She gave a long sigh of relief.

'Thank God. I thought I'd missed you.'

He leaned over and closed the door very quietly.

'How many are there?'

'Six. Two in the fields opposite. Two going from house to house in the village. Two in the cottage – one upstairs, dusting Claire's bedroom for fingerprints, and a policewoman downstairs. I told her I was going out. She tried to stop me but I said it was my one day off this week and I'd do as I pleased. I left by the back door and worked my way round to the road.'

'Did anybody see you?'

'I don't think so.' She blew warmth on her hands and rubbed them. 'I suggest we drive, Mr Jericho. And don't go back into Bletchley, whatever you do. I overheard them talking. They're stopping all cars on the main road out of town.'

She slid further down the seat so that she was invisible from outside the car unless someone came right up to the window. Jericho turned on the engine and the Austin rolled forwards. If they couldn't go back to Bletchley, he thought, then really he had no choice except to drive straight ahead.

They came round the curve and the road was clear. The turning to the cottage was on the left, deserted, but as they came level with it a policeman suddenly stepped out from the hedge opposite and held up his hand. Jericho hesitated and then pressed his foot down on the accelerator. The policeman stepped smartly out of the way and Jericho had a momentary impression of an outraged brick-red face. Then they were dropping down into the hollow and rising again and passing through the village. Another policeman was talking to a woman on the doorstep of her thatched cottage and he turned to stare at them. Jericho trod on the accelerator again and soon the village was behind them and the road was corkscrewing down into another leafy hollow. They rose into Shenley Church End, passed the White Hart Inn, where Jericho used to live, and then a church, and almost at once they had to stop at the junction of the A5.

Jericho glanced in his mirror to check there was no one behind them. It seemed safe enough. He said to Hester: 'You can get up now.' He was in a daze. He couldn't believe what he was doing. He waited to let a couple of lorries go by, indicated, and then swung left on to the old Roman road. It ran straight and true ahead of them, northwest, for as far as they could see. Jericho changed up a gear, the Austin gathered speed, and they were clear.

Wartime England opened up before them – still the same but somehow subtly different: a little bit smudged, a little bit knocked about, like a prosperous estate going fast to ruin, or a genteel elderly lady fallen on hard times.

They didn't encounter any bomb damage until they reached the outskirts of Rugby, where what looked from a distance to be a ruined abbey turned out to be the roofless shell of a factory, but the depredations of war were everywhere. Fences beside the road, after three years without repairs, were sagging or collapsed. The gates and railings had gone from the fine country parks to be melted down for munitions. The houses were shabby. Nothing had been painted since 1940. Broken windows were boarded over, ironwork was rusted or coated in tar. Even the inn signs were blistered and faded. The country was degraded.

And we, too, thought Jericho, as they overtook yet another stooped figure trudging beside the road, don't we look slightly worse each year? In 1940 there had at least been the galvanising energy unleashed by the threat of invasion. And in 1941 there had been some hope when Russia and then America had entered the war. But 1942 had dragged into 1943, the U-boats had wrought murder on the convoys, the shortages had worsened and, despite the victories in Africa and on the eastern front, the war had begun to look endless – an unbroken, unheroic vista of rationing and exhaustion. The villages seemed almost lifeless – the men away, the women drafted into factories – while in Stony Stratford and in Towcester the few people who were about had mostly formed into queues outside shops with empty windows.

Beside him, Hester Wallace was silent, monitoring their progress with obsessive interest on Atwood's atlas. Good, he thought. With all the signposts and place names taken down, they would have no idea where they were if they once got lost. He didn't dare drive too quickly. The Austin was unfamiliar and (he was discovering) idiosyncratic. From time to time the cheap wartime petrol caused it to emit a loud bang. It tended to drift towards the centre of the road, and the brakes weren't too hot, either. Besides, a private car was such a rarity, he feared some officious policeman would pull them over if they went too fast and demand to see their papers.

He drove on steadily for more than an hour until, just before a market town she declared was Hinckley, she told him to turn off right on to a narrower road.

They had left Bletchley under a clear sky but the further north they had gone, the darker it had become. Grey clouds heavy with snow or rain had rolled across the sun. The tarmac pushed across a bleak, flat landscape, with not a vehicle to be seen, and for a second time Jericho experienced the curious sense that history was going backwards, that not for a quarter of a century could the roads have been this empty.

Fifteen miles further on she made him turn right again and suddenly they were climbing into much more hilly country, thickly wooded, with startling outcrops of bare rock striped white by snow.

'What place is this?'

'Charnwood Forest. We're almost there. You'd better pull over in a minute. Here, look,' she said, pointing to a deserted picnic area set just off the road. 'Here will do. I shan't be long.'

She hauled her bag from the back seat and set off towards the trees. He watched her go. She looked like a farm boy in her jacket and trousers. What was it Claire had said? 'She's got a bit of a crush on me? More than a bit, he thought, much more than a bit, to risk so much. It struck him that she was almost the exact physical opposite of Claire, that where Claire was tall and blonde and voluptuous, Hester was short and dark and skinny. Rather like him, in fact. She was changing her clothes behind a tree which wasn't quite wide enough and he got a sudden glimpse of her thin white shoulder. He looked away. When he looked back she was emerging from the dark woodland in an olive-green dress. The first drop of rain plopped on to the windscreen just as she got back into the car.

'Drive on then, Mr Jericho.' She found their position on the atlas again and rested her finger on it.

His hand paused on the ignition key. 'Do you think, Miss Wallace,' he said, hesitantly, 'in view of the circumstances, we might now risk first-name terms?'

She gave him a faint smile. 'Hester.'

'Tom.'

They shook hands.

They followed the road through the forest for about five miles and then the trees thinned and they were into high, open country. The rain and melted snow had turned the narrow lane into a mud track and for five minutes they were forced to crawl in second gear behind a pony and trap. At last the driver raised his whip in apology and turned off to the right, towards a tiny village with curls of smoke rising from half a dozen chimneys, and very soon afterwards Hester shouted: 'There!'

If they hadn't been travelling so slowly, they might have missed it: a pair of lodge gates, a private road with a red-and-white pole slung across it, a sentry box, a cryptic sign: WOYG, BEAUMANOR.

War Office 'V Group, Beaumanor, 'Y being the code name for the wireless interception service.

'Here we go.'

Jericho had to admire her nerve. While he was still fumbling sweatily for his pass, she had leaned across him to proffer hers to the guard and had announced briskly that they were expected. The Army private checked her name off on a clipboard, went round to the back of the car to make a note of their registration number, returned to the window, gave Jericho's card a cursory glance, and nodded them in.

Beaumanor Hall was another of those huge, secluded country houses that had been commandeered by the military from their grateful, almost bankrupt owners, and that would never, Jericho guessed, return to private use. It was early Victorian, with an avenue of dripping elms to one side and a stable yard to the other, into which they were directed. They drove under a fine arch. Half a dozen giggling ATS girls, their coats held over their heads like tents to ward off the rain, ran out in front of them and disappeared into one of the buildings. The courtyard held a couple of small Morris commercial trucks and a row of BSA motorcycles. As Jericho parked, a uniformed man hurried over to them carrying a vast and battered umbrella.

'Heaviside,' he said, 'Major Heaviside, as in the eponymous layer. And you must be Miss Wallace and you must be…?'

'Tom Jericho.'

'Mr Jericho. Excellent. Splendid.' He shook their hands vigorously. 'This is a treat for us, I must say. A visit from head office to the country cousins. Commander sends a thousand sorrows and says d'you mind if I do the honours? He'll try and catch us later. 'Fraid you've missed lunch, but tea? Cup of tea? Filthy weather…"

Jericho had been braced for some suspicious questions, and had used the journey to rehearse some careful answers, but the major merely ushered them under his leaking umbrella and guided them into the house. He was young, tall and balding, with spectacles so smeared with debris it was a wonder he could see through them. He had sloping shoulders, like a bottle, and the collar of his tunic was blanched white with dandruff. He took them into a cold and musty drawing room and ordered tea.

By now he'd finished his potted history of the house ('designed by the same bloke who built Nelson's Column, so they tell me') and was well embarked on a detailed history of the wireless interception service ('started out in Chatham till the bombing got too bad…'). Hester was nodding politely. A woman Army private brought them tea as thick and brown as shoe polish and Jericho sipped it and glanced impatiently around the empty walls. There were holes in the plaster where the picture hooks had been pulled out, and grimy shadows traced the outlines of large frames, now removed. An ancestral seat without ancestors, a house without a soul. The windows looking out on to the garden were crossed with strips of sticky tape.

He pointedly took out his watch and opened it. Almost three o'clock. They would need to be moving soon.

Hester noticed he was fidgeting. 'Perhaps,' she said, leaping into a brief lull in the major's monologue, 'we might take a look around?'

Heaviside looked startled and clattered his teacup into his saucer. 'Oh, crumbs, sorry. Right. If you're fit, then, we'll make a start.'

The rain was mixed with snow now, and the wind was blowing it hard, in waves, from the north. It lashed their faces as they came around the side of the big house and as they picked their way through the mud of a flattened rose garden they had to raise their arms against it, like boxers warding off blows. There was an odd keening, howling noise, like nothing Jericho had ever heard before, coming from beyond a wall.

'What the devil's that?'

'The aerial farm,' said Heaviside.

Jericho had only visited an intercept station once before, and that had been years ago, when the science was still in its infancy: a shack full of shivering Wrens perched on top of the cliffs near Scarborough. This was of a different order. They went through a gate in the wall and there it was – dozens of radio masts laid out in odd patterns, like the stone circles of the Druids, across several acres of fields. The metal pylons were bound together by thousands of yards of cable. Some of the taut steel hummed in the wind, some screamed.

'Rhombic and Beveridge configurations,' shouted the major above the racket. 'Dipoles and quadra-hedrons… Look!' He tried to point and his umbrella was abruptly snapped inside out. He smiled hopelessly and waved it in the direction of the masts. 'We're about three hundred feet up here, hence this bloody wind. The farm's got two main harvests, can you see? One's pointing due south. That picks up France, the Med, Libya. The other's targeted east to Germany and the Russian front. The signals go by coaxial cables to the intercept huts.' He spread his arms wide and bellowed, 'Beautiful, isn't it? We can pick up everything for the best part of a thousand miles.' He laughed and waved his hands as if he were conducting an imaginary choir. 'Sing to me, you buggers.'

The wind slashed sleet in their faces and Jericho cupped his hands to his ears. It felt as though they were interfering with nature, tapping into some rushing elemental force they had no business dabbling in, like Frankenstein summoning down lightning into his laboratory. Another gust of wind knocked them backwards and Hester clutched at his arm for support.

'Let's get out of here,' yelled Heaviside. He gestured for them to follow him. Once they were on the other side of the wall they had some shelter from the wind. An asphalt road girdled what looked, at a distance, to be an estate village nestling in the grounds of the big house: cottages, farm sheds, a greenhouse, even a cricket pavilion with a clock tower. All dummy frontages, explained Heaviside, cheerfully, designed to fool German air reconnaissance. This was where the work of interception was done. Was there anything they were especially interested in?

'How about the eastern front?' said Hester.

'Eastern front?' said Heaviside. 'Fine.'

He bounded ahead of them through the puddles, still trying to shake out his broken umbrella. The rain worsened and their fast walk turned into a run as they sprinted for the hut. The door banged shut behind them.

'We rely on the feminine element, as you can see,' said Heaviside, taking off his spectacles and drying them on the corner of his tunic. 'Army girls and civilian women.' He replaced his glasses and blinked around the hut. 'Good afternoon,' he said to a stout woman with sergeant's stripes. 'The supervisor,' he explained, then added in a whisper: 'Bit of a dragon.'

Jericho counted twenty-four wireless receivers, arranged in pairs, on either side of a long aisle, each with a woman hunched over it wearing headphones. The room was quiet apart from the hum of the machines and the occasional rustle of intercept forms.

'We've three types of sets,' Heaviside went on quietly. 'HROs, Hallicrafter 28 Skyriders and American AR-88s. Each girl has her own frequencies to patrol, though we'll double back if things get busy.'

'How many people d'you have working here?' asked Hester.

'Couple of thousand.'

'And you intercept everything?'

'Absolutely. Unless you tell us not to.'

'Which we never do.'

'Right, right.' Heaviside's bald head was glistening with rainwater. He bent forwards and shook himself vigorously, like a dog. 'Except that time the other week, of course.'

Afterwards, what Jericho would remember most was how coolly she handled it. She didn't even blink. Instead she actually changed the subject and asked Heaviside how fast the girls had to be ('we insist on a speed of ninety Morse characters a minute, that's the absolute minimum') and then the three of them began to stroll down the central aisle.

'These are sets tuned to the eastern front,' said Heaviside, when they were about halfway down. He stopped and pointed to the elaborate pictures of vultures stuck on the side of several of the receivers.

'Vulture's not the only German Army key in Russia, of course. There's Kite and Kestrel, Smelt for the Ukraine -'

'Are the nets particularly active at the moment?' Jericho felt it was time he should say something.

'Very much so, since Stalingrad. Retreats and counterattacks all along the front. Alarms and excursions. You've got to hand it to these Reds, you know – they can't half fight.'

Hester said casually: 'It would have been a Vulture station you were told not to intercept?'

That's right.'

'And this would have been around the 4th of March?'

'Bang on. About midnight. I remember because we'd just sent four long signals and were feeling fairly well chuffed when your chap Mermagen comes on the blower in a frightful panic and says: "No more of that, thanks very much, not now, not tomorrow, not for ever more.

'Any reason?'

'No reason. Just stop. Thought he was going to have a heart attack. Oddest damned thing I ever heard.'

'Perhaps,' suggested Jericho, 'knowing you were busy, they wanted to knock out low-priority traffic?'

'Balls,' said Heaviside, 'pardon me, but really!' His professional pride was wounded. 'You can tell your Mr Mermagen from me that it was nothing we couldn't handle, was it, Kay?' He patted the shoulder of a strikingly pretty ATS operator, who took off her headphones and pushed back her chair. 'No, no, don't get up, didn't mean to interrupt. We were just discussing our mystery station.' He rolled his eyes. 'The one we're not supposed to hear.'

'Hear?' Jericho looked at Hester sharply. 'You mean it's still broadcasting?'

'Kay?'

'Yes, sir.' She had a rather melodious Welsh accent. 'Not so often now, sir, but he was awful busy last week.' She hesitated. 'I don't, like, try to listen, on purpose, sir, but he does have the most beautiful fist. Real old school. Not like some of the kids – she spat out the word '- they're using nowadays. Nearly as bad as the Italians, they are.'

'A man's style of Morse,' said Heaviside pompously, 'is as distinctive as his signature.'

'And what is his style?'

'Very fast but very clear,' said Kay. 'Rippling, I'd say. Fist like a concert pianist, he has.'

'Think she rather fancies this chap, don't you, Mr Jericho?' Heaviside laughed and gave her shoulder another pat. 'All right, Kay. Good work. Back to it.'

They moved on. 'One of my best,' he confided. 'Can be pretty ghastly, you know, eight hours listening at a stretch, just taking down gibberish. Specially at night, in the winter. Bloody freezing out here. We have to issue 'em with blankets. Ah, now, here, look: here's one coming in.'

They stood at a discreet distance behind an operator who was frantically copying down a message. With her left hand she kept fractionally adjusting the dial on the wireless set, with her right she was fumbling together message forms and carbon paper. The speed with which she then started to take down the message was astonishing. 'GLPES,' read Jericho over her shoulder, 'KEMPG NXWPD

'Two forms,' said Heaviside. 'Log sheet, on which she records the whispers: that's tuning messages, Q-code and so forth. And then the red form which is the actual signal.'

'What happens next?' whispered Hester.

'There are two copies of each form. Top copy goes to the Teleprinter Hut for immediate transmission to your people. That's the hut we passed that looks like the cricket pavilion. The other copies we keep here, in case there's a garble or something goes missing.'

'How long do you keep them?'

'Couple of months.'

'Can we see?'

Heaviside scratched his head. 'If you want. Not much to it, though.'

He led them to the far end of the hut, opened a door, turned on the light and stood back to show them the interior. A walk-in cupboard. A bank of about a dozen dark green filing cabinets. No window. Light switch on the left.

'How are they arranged?' asked Jericho.

'Chronologically.' He closed the door.

Not locked, noted Jericho, continuing his inventory. And the entrance not really visible, except to the four operators nearest to it. He could feel his heart beginning to thump.

'Major Heaviside, sir!'

They turned to find Kay standing, beckoning to them, one of her headphones pressed to her ear.

'My mystery piano player, sir. He's just started doing his scales again, sir, if you're interested.'

Heaviside took the headset first. He listened with a judicious expression, his eyes focused on the middle distance, like an eminent doctor with a stethoscope being asked to give a second opinion. He shook his head and shrugged and passed the headphones to Hester.

'Ours not to reason why, old chap,' he said to Jericho. When it was Jericho's turn, he removed his scarf and placed it carefully on the floor next to the cable form that connected the wireless set to the aerials and the power supply. Putting on the headphones was rather like putting his head under water. There was a strange rush of sounds. A howl that reminded him of the wind in the aerial farm. A gunfire crackle of static. Two or three different and very faint Morse transmissions braided together. And suddenly, and most bizarrely, a German diva singing an operatic aria he vaguely recognised as being from the second act of Tannhauser. 'I can't hear anything.'

'Must have drifted off frequency,' said Heaviside. Kay turned the dial minutely anticlockwise, the sound wowed up and down an octave, the diva evaporated, more gunfire, and then, like stepping into an open space, a rapid, staccato dah-dah-dah-dah-dah of Morse, pulsing clearly and urgently, more than a thousand miles distant, somewhere in German-occupied Ukraine.

They were halfway to the Teleprinter Hut when Jericho raised his hand to his throat and said, 'My scarf.'

They stopped in the rain.

'I'll get one of the girls to bring it over.'

'No, no, I'll fetch it, I'll catch you up.'

Hester took her cue. 'And how many machines did you say you have?' She began to walk on.

Heaviside hesitated between the two of them, then hurried after Hester. Jericho could have kissed her. He never heard the major's answer. It was whipped away by the wind.

You are calm, he told himself, you are confident, you are doing nothing wrong.

He went back into the hut. The woman sergeant had her fat back to him, leaning over one of the interceptors. She never saw him. He walked swiftly down the central aisle, looking straight ahead, and let himself into the storeroom. He closed the door behind him and turned on the light.

How long did he have? Not long.

He tugged at the first drawer of the first filing cabinet. Locked. Damn it. He tried it again. Wait. No, it wasn't locked. The cabinet was fitted with one of these irritating anti-tilt mechanisms, which prevented two drawers being opened at once. He looked down and saw that the bottom drawer was protruding slightly. He closed it gently with his foot and to his relief the top drawer slid open.

Brown cardboard folders. Bundles of smudged carbons, held together by metal paperclips. Log sheets and W/T red forms. Day, Month and Year in the top right-hand corner. Meaningless jumbles of handwritten letters. This folder for 15 January 1943.

He stepped back and counted quickly. Fifteen four-drawer cabinets. Sixty drawers. Two months. Roughly a drawer a day. Could that be right?

He strode over to the sixth cabinet and opened the third drawer down. February the 6th. Bingo.

He held the image of Hester Wallace's neat notation steady in his mind. 6.2./1215. 9.2/1427. 20.27 1807. 2.3./1639, 1901…

It would have helped if his fingers hadn't swollen to the size of sausages, if they weren't shaking and slippery with sweat, if he could somehow catch his breath.

Someone must come in. Someone must hear him, surely, opening and closing the metal drawers like organ stops, pulling out two, three, four cryptograms and the log sheets, too (Hester had said they'd be useful), stuffing them into his inside coat pocket, five, six – dropped it, damn – seven cryptograms. He almost gave up at that – 'Quit while you're ahead, old love' -but he needed the final four, the four Claire had hidden in her room.

He opened the top drawer of the thirteenth filing cabinet, and there they were, towards the back, virtually in sequence, thank you, God.

A footstep outside the storeroom. He grabbed the logs and red forms and had just about got them into his pocket and the drawer shut when the door opened to silhouette the trim figure of Kay the intercept girl.

'I thought I saw you come in,' she said, 'only you left your scarf, see?' She held it up and closed the door behind her, then slowly advanced down the narrow room towards him. Jericho stood paralysed with an idiot grin on his face.

'I don't mean to bother you, sir, but it is important, isn't it?' Her dark eyes were wide. He dimly registered again that she was very pretty, even in her Army uniform. The tunic was belted tight at her waist. Something about her reminded him of Claire.

'I'm sorry?'

'I know I shouldn't ask, sir – we're never meant to ask, are we? – but, well, is it? Only no one ever tells us, see? Rubbish, that's all it is to us, just rubbish, rubbish, all day long. And all night, too. You try to go to sleep and you can still hear it – beep-beep-bloody-beep. Drives you barmy after a bit. I joined up, see, volunteered, but it's not what I expected, this place. Can't even tell my mum and dad.' She had come up very close to him. 'You are making sense of it? It is important? I won't tell,' she added, solemnly, 'honest.' 'Yes,' said Jericho. 'We are making sense of it, and it is important. I promise you.'

She nodded to herself, smiled, looped his scarf around his neck and tied it, then walked slowly out of the storeroom, leaving the door open. He gave it twenty seconds, then followed her. Nobody stopped him as he went out through the hut and into the rain.

4

Heaviside didn't want them to leave. Jericho tried feebly to protest – the light was bad, he said, they had a long journey ahead, they had to beat the blackout -but Heaviside was horrified. He insisted, insisted they at least take a look at the direction finders and the highspeed Morse receivers. He was so enthusiastic, he looked as though he might burst into tears if they said no. And so they trailed meekly after him across the slick wet concrete, first to a row of wooden huts dressed up to look like a stable block and then to another fake cottage.

The chorus of the aerial farm sang weirdly in the background, Heaviside became increasingly excited describing abstruse technicalities of wavelength and frequency, Hester pretended heroically to be interested and carefully avoided meeting Jericho's eye, and all the time Jericho walked around unhearing, in a cocoon of anxiety, nerved for the distant sounds of discovery and alarm. Never had he been more desperate to get away from anywhere. From time to time his hand stole into his inside coat pocket, and once he left it there, reassured to feel the roughness of the intercepts safely between his fingers, until he realised he was doing a passable impersonation of Napoleon, whereupon he promptly snatched it out again.

As for Heaviside, such was his pride in Beaumanor's work, he clearly would have kept them there for another week if he could. But when, an interminable half-hour later, he suggested a visit to the motor pool and the auxiliary generators, it was Hester, so cool until then, who finally snapped and said, rather too firmly in retrospect, that no, thank you, but really they did have to get going.

'Honestly? It's a heck of a long way to have come for just a couple of hours.' Heaviside looked mystified. 'The commander will be disappointed to miss you.'

'Alas,' said Jericho. 'Some other time.'

'Up to you, old boy,' said Heaviside huffily. 'Don't want to press ourselves on you.' And Jericho cursed himself for hurting his feelings.

He walked them round to their car, halting on the way to point out an antique ship's figurehead of an admiral, perched on top of an ornamental horse trough. Some wit had draped a pair of Army knickers over the admiral's sword and they hung limply in the raw damp. 'Cornwallis,' said Heaviside. 'Found him in the grounds. Our lucky charm.'

When they said goodbye he shook hands with them each in turn, Hester first, then Jericho, and saluted as they got into the Austin. He turned as if to go, then froze, and suddenly ducked down to the window.

'What was it you said you did again, Mr Jericho?'

'Actually, I didn't.' Jericho smiled and turned the engine on. 'Cryptanalytic work.'

'Which section?'

'Can't say, I'm afraid.'

He jammed the gear stick into reverse and executed a clumsy three-point turn. As they pulled away he could see Heaviside in the rear-view mirror, standing in the rain, his hand protecting his eyes, watching them. The curve of the drive took them off to the left and the image vanished.

'Pound to a penny,' muttered Jericho, 'he's on his way to the nearest telephone.'

'You got them?'

He nodded. 'Let's wait till we get clear of here.'

Out through the gates, along the lane, past the village, towards the forest. The rain was blowing across the dark slope of woodland in ghostly white columns, like the banners of a phantom army. A large and lonely bird was flying through the cloudburst, very high and far away. The windscreen wipers scudded back and forth. The trees closed in around them.

'You were very good,' said Jericho.

'Until the end. By the end it was unendurable, not knowing if you'd managed it.'

He started to tell her about the storeroom, but then he noticed a track coming up, leading off from the side of the road into the privacy of the wood.

The perfect spot.

They bounced along the rough trail for about a hundred yards, plunging into puddles that turned out to be potholes a foot deep. Water fountained out on either side of them, tearing against the underside of the chassis. It spouted through a hole at Hester's feet and drenched her shoes. When at last the headlights showed a patch of bog too wide to negotiate, Jericho turned off the engine.

There was no sound except for the pattering of the rain on the thin metal roof. Overhanging branches blotted out the sky. It was almost too dark to read. He turned on the interior light.

'VVVADU QSA?K,' said Jericho, reading off the whispers on the first log sheet. 'Which, if I remember my days in traffic analysis, roughly translates as: This is station call sign ADU requesting reading of my signal strength, over.' He ran his finger down the carbon copy. Q-code was an international language, the Esperanto of wireless operators; he knew it off by heart. 'And then we get VVVCPQ BT QSA4 QSA?K. This is station call-sign CPQ, break, your signal strength is fine, what is my signal strength? Over.'

'CPQ,' said Hester, nodding. 'I recognise that call sign. That has something to do with Army High Command in Berlin.'

'Good. One mystery solved, then.' He returned his attention to the log sheet. 'WVADU QSA3 QTCI K: Smolensk to Berlin, your signal strength is reasonable, I have one message for you, over. QRV, says Berlin: I am ready. QXH K: broadcast your traffic, over. Smolensk then says QXA109: my message consists of 109 cipher groups.'

Hester fluttered the first cryptogram triumphantly. 'Here it is. One hundred and nine exactly.'

'OK. Fine. So that goes through – straight away, presumably, because Berlin replies: VVVCPQ R QRU HHVA. Message received and understood, I have nothing for you, Heil Hitler and good night. All very smooth and methodical. Right out of the manual.'

'That girl in the Intercept Hut said he was precise.'

'What we don't have, unfortunately, is Berlin's replies.' He riffled through the log sheets. 'Easy contact on the 9th as well, and again on the 20th. Ah,' he said, 'now on the 2nd of March it looks to have been more tricky.' The form was indeed a mass of terse dialogue. He held it up to the light. Smolensk to Berlin: QZE, QRJ, QRO. (Your frequency is too high, your signals are too weak, increase your power.) And Berlin snapping back: QWP, QRXIO (observe regulations, wait ten minutes) and finally an exasperated QRX (shut up). 'Now this is interesting. No wonder they suddenly start to sound like strangers.' Jericho squinted at the carbon copy. 'The call sign in Berlin has changed.'

'Changed? Absurd. Changed to what?'

'TGD.'

'What?. Let me see that.' She snatched the form out of his hand. 'That's not possible. No, no. TGD simply isn't a Wehrmacht call sign.'

'How can you be sure?'

'Because I know it. There's a whole Enigma key named after TGD. It's never been broken. It's famous.' She had started to wind a lock of hair nervously around her right index finger. 'Notorious might be a better word.'

'What is it?'

'It's the call sign of Gestapo headquarters in Berlin.'

'Gestapo?' Jericho fumbled through the remaining log sheets. 'But all the messages from March the 2nd onwards,' he said, 'that's eight out of the eleven, all the long ones, including the four in Claire's room – they're all addressed to that sign.' He gave the forms to her so she could check for herself and sat back in his seat.

A gust of wind stirred the branches above them, sending a shower of rainwater rattling like a volley across the windscreen.

'Let's try and construct a thesis,' said Jericho after a minute or two, as much to hear a human voice as anything. The random pattering of the downpour and the crepuscular gloom of the forest were beginning to affect his nerves. Hester had pulled her feet up from the sodden floor and was huddled up very small on the front seat, staring out at the forest, hugging her legs, occasionally massaging her toes through her damp stockings.

'March the 4th is the key day,' he went on. (Where was I on 4 March? In another world: reading Sherlock Holmes in front of a Cambridge gas fire, avoiding Mr Kite and learning to walk again) 'Up to that day, everything is proceeding normally. A signals unit hibernating in the Ukraine, dormant all winter, has come to life in the warmer weather. First, a few signals to Army HQ in Berlin, and then a burst of longer traffic to the Gestapo -'

'That's not normal,' said Hester scathingly. 'An Army unit transmitting reports in a Russian-front Enigma key to the headquarters of the secret police? Normal? I'd call that unprecedented.'

'Quite.' He didn't mind being interrupted. He was glad of a sign she was listening. 'In fact, it's so unprecedented, someone at Bletchley wakes up to what's happening and starts to panic. All previous signals are removed from the Registry. And just before

midnight on that same day your Mr Mermagen telephones Beaumanor and tells them to stop interception. Ever happen before?'

'Never.' She paused, then moved her shoulder slightly in concession. 'Well, all right, maybe, when traffic's very heavy, a low-priority target might be neglected for a day or so. But you saw the size of Beaumanor. And that's not as big as the RAF's station at Chicksands. And there must be a dozen smaller places, maybe more. We're always being told by people like you that the whole point of the exercise is to monitor everything?

He nodded. This was true. It had been their philosophy from the beginning: be inclusive, miss nothing. It isn't the big boys who give you the cribs – they're too good. It's the little fellows – the long-forgotten incompetents stuck in out-of-the-way places, who always begin their messages 'situation normal, nothing to report' and then use the same nulls in the same places, or who habitually encipher their own call-signs, or who set the rotors every morning with their girlfriend's initials…

Jericho said: 'So he wouldn't have told them to stop on his own authority?'

'Miles? God, no.'

'Who gives him his orders?'

'That depends. Hut 6 Machine Room, usually. Sometimes the Hut 3 Watch. They decide priorities.'

'Could he have made a mistake?'

'In what sense?'

'Well, Heaviside said Miles called Beaumanor just before midnight on the 4th in a panic. I was wondering: what if Miles had been told earlier in the day that this unit was no longer to be intercepted, but forgot to pass on the message.'

'Eminently possible. Likely, in fact, knowing Miles. Yes, yes of course.' Hester turned round to face him. 'I see what you're driving at. In the time between Miles being told to pull the plug and the order reaching Beaumanor, four more messages had been intercepted.'

'Exactly. Which came into Hut 6 late on the night of the 4th. But by then the order had already been issued that they weren't to be decoded.'

'So they just got caught up in the bureaucracy and were passed along the line.'

'Until they ended up in the German Book Room.'

'In front of Claire.'

'Undecrypted.'

Jericho nodded slowly. Undecrypted. That was the crucial point. That explained why the signals in Claire's bedroom had showed no signs of damage. There had never been any strips of Type-X decode gummed to their backs. They had never been broken.

He peered into the wood but he didn't see trees, he saw the German Book Room on the morning after the night of 4 March, when the cryptograms would have arrived to be filed and indexed.

Would Miss Monk herself have rung the Hut 6 duty officer, or would she have delegated the task to one of her girls? 'We've got four orphan intercepts here, without the solutions. What, pray, are we supposed to do with them?' And the reply would have been – what?

Oh, Christ! File them? Forget them? Dump them in the bin marked CONFIDENTIAL WASTE?

Only none of those things had happened.

Claire had stolen them instead.

'In theory?' Weitzman had said. ' On an average day? A girl like Claire would probably see more operational detail about the German armedl forces than Adolf Hitler. Absurd, isn't it?'

Ah, but they weren't supposed to read it, Walter, that was the point. Well-bred young ladies wouldn't dream of reading someone else's mail, unless they were told to do so for King and country. They certainly wouldn't read it for themselves. That was the reason why Bletchley employed them.

But what was it Miss Monk had said of Claire? 'She'd really become much more attentive of late…' Naturally she had. She had begun to read what was passing through her hands. And at the end of February or the beginning of March she had seen something that had changed her life. Something to do with a German rear-echelon signals unit whose wireless operator played Morse code to the Gestapo as if it were a Mozart sonata. Something so utterly 'un-boring, darling', that when Bletchley had decided they couldn't bear to read the traffic any more, she had felt compelled to steal the last four intercepts herself.

And why had she stolen them?

He didn't even need to pose the question. Hester had reached the answer ahead of him, although her voice was faint and disbelieving and almost drowned out by the rain.

'She stole them to read them.'

She stole them to read them. The answer slid beneath the random pattern of events and fitted it like a crib.

She stole the cryptograms to read them.

'But is it really feasible?' asked Hester. She seemed bewildered by the destination to which her logic had led her. 'I mean, could she really have done it?'

'Yes. It's possible. Hard to imagine. Possible.'

Oh, the nerve of it, thought Jericho. Oh, the sheer breathtaking bloody nerve of it, the cool deliberation with which she must have plotted it. Claire, my darling, you really are a wonder.

'But she couldn't have managed it on her own,' he said, 'not locked away at the back of Hut 3. She'd have needed help.'

'Who?'

He raised his hands from the steering wheel in a hopeless gesture. It was hard to know where to begin. 'Someone with access to Hut 6 for a start. Someone who could look up the Enigma settings for German Army key Vulture on March the 4th.'

'Settings?'

He glanced at her in surprise, then realised that the actual workings of an Enigma was not the sort of information she would have needed to know. And in Bletchley, what you didn't need to know you were never told.

'Walzenlage,' he said. ' Ringstellung. Stecker-verbindungen. Wheel order, ring setting and cross-plugging. If Vulture was being read every day, they'd already have had those in Hut 6.'

'Then what would you have had to do?'

'Get access to a Type-X machine. Set it up in exactly the right way. Type in the cryptograms and tear off the plaintext.'

'Could Claire have done that?'

'Almost certainly not. She'd never have been allowed anywhere near the decoding room. And anyway she wasn't trained.'

'So her accomplice would have needed some skill?'

'Skill, yes. Arid nerve. And time, come to that. Four messages. A thousand cipher groups. Five thousand individual characters. Even an expert operator would need the best part of half an hour to decode that much. It could have been done. But she would have needed a superman.'

'Or woman.'

'No.' He was remembering the events of Saturday night: the sound downstairs in the cottage, the big male footprints in the frost, the cycle tracks and the red rear light of the bicycle shooting away from him into the darkness. 'No. It's a man.'

If only I'd been thirty seconds quicker, he thought. I'd have seen his face.

And then he thought: Yes, and maybe got a bullet in my own for my trouble: a bullet from a stolen Smith and Wesson.38, manufactured in Springfield, Massachusetts.

He felt a sudden prickle of ice-cold moisture on the back of his wrist and glanced up. He followed its trajectory to a spot in the roof, just before the windscreen. As he watched, another dark bubble of rainwater slowly swelled, ripened to a rich rust colour, and dropped.

Shark.

He realised guiltily he had nearly forgotten it.

'What's the time?'

'Almost five.'

'We should be getting back.'

He rubbed at his hand and reached for the ignition.

The car wouldn't start. Jericho twisted the key back and forth and pumped away frantically at the accelerator but all he managed to coax from the engine was a dull turning noise.

'Oh, hell!'

He turned up his collar, got out and went round to the boot. As he opened the lid a brace of pigeons took off behind him, wings snapping like firecrackers. There was a starting handle under the spare can of petrol and he inserted that into the hole in the front bumper.' You do this the wrong way, lad,' his stepfather had told him, 'and you can break your wrist." But which was the right way? Clockwise or anticlockwise? He gave the handle a hopeful tug. It was horribly stiff.

'Pull out the choke,' he shouted to Hester, 'and press your foot down on the third pedal if she starts to fire.'

The little car rocked as she slid across into the driver's seat.

He bent to his task again. The forest floor was only a couple of feet from his face, a pungent brown carpet of decaying leaves and fir cones. He heaved a couple more times until his shoulder ached. He was beginning to sweat now, perspiration mingling with the rainwater, dripping off the end of his nose, trickling down his neck. The insanity of their whole undertaking seemed encapsulated in this moment. The greatest convoy battle of the war was about to start, and where was he? In some primeval bloody forest in the middle of bloody nowhere poring over stolen Gestapo cryptograms with a woman he barely knew. What in the name of reason did they think they were doing? They must be – he tightened his grip – crazy… He jerked viciously on the starting handle and suddenly the engine caught, spluttered, nearly died, then Hester revved it loudly. The sweetest sound he'd ever heard, it split the forest. He slung the handle into the boot and slammed the lid.

The gearbox whined as he reversed along the track towards the road.

The overhanging branches made a tunnel of the soaking lane. Their headlights glinted on a film of running water. Jericho drove slowly around and around the same course, trying to find some landmark in the gloom, trying not to panic. He must have taken a wrong turning coming out of the clearing. The steering wheel beneath his hands felt as wet and slippery as the road. Eventually they came to a crossroads beside a vast and decaying oak. Hester bent her head again to the map. A lock of long black hair fell across her eyes. She used both hands to pile it up. She clenched a pin between her teeth and muttered through it: 'Left or right?'

'You're the navigator.'

'And you're the one who decided to drive us off the main road.' She skewered her hair savagely back in place. 'Go left.'

He would have chosen the other way but thank God he didn't because she was right. Soon the road ahead began to brighten. They could see patches of weeping sky. He pressed his foot down and the speedometer touched forty as they passed out of the forest and into the open. When, after a mile or so, they came to a village, she told him to pull up outside the tiny post office.

'Why?'

'I need to find out where we are.'

'You'd better be quick.'

'I've really no intention of sight-seeing.'

She slammed the door behind her and ran through the rain, sidestepping the puddles with a gym mistress's agility. A bell tinkled inside the shop as she opened the door.

Jericho glanced ahead, then checked in his mirror. The village appeared to consist of nothing more than this one street. No parked vehicles that he could see. No one about. He guessed that a private car, especially one driven by a stranger, would be a rarity, a talking-point. In the little red-brick cottages and the half-timbered houses he could already imagine the curtains being twitched back. He turned off the windscreen wipers and sank lower in his seat. For the twentieth time his hand went to the bulge of cryptograms in his inside pocket.

Two Englands, he thought. One England – this one – familiar, safe, obvious. But now another, secret England, secluded in the grounds of stately houses -Beaumanor, Gayhurst, Woburn, Adstock, Bletchley – an England of aerial farms and direction finders, clattering bombes and, soon, the glowing green and orange valves of Turing machines ('it should make the calculations a hundred times, maybe a thousand times as fast'}. A new age beginning to be born in the parklands of the old. What was it that Hardy had written in his Apology? 'Real mathematics has no effect on war. No one has yet discovered any warlike purpose to be served by the theory of numbers.' The old boy couldn't guess the half of it.

The bell tinkled again and Hester emerged from the post office holding a newspaper over her head like an umbrella. She opened the car door, shook the paper and threw it, not very gently, into his lap.

'What's this for?' It was the Leicester Mercury, the local rag: that afternoon's edition.

'They print appeals for help, don't they? From the police? When someone is missing?'

It was a good idea. He had to concede it. But although they checked the paper carefully – twice, in fact – they could find no photograph of Claire and no mention of the hunt for her.

Dropping southwards, heading for home. A different route for the return journey, more easterly – this was Hester's plan. To keep their spirits up, she occasionally recited the names of the villages and checked them in the gazetteer as they rattled down their empty high streets. Oadby, she said, ('note the early English to Perpendicular church'), Kibworth Harcourt, Little Bowden, and on across the border out of Leicestershire and into Northamptonshire. The sky over the distant pale hills brightened from black to grey and finally to a kind of glossy, neutral white. The rain slowed, then stopped. Oxendon, Kelmarsh, Maidwell… Square Norman towers with arrow-slits, thatched pubs, tiny Victorian railway stations nesting in a bosky countryside of high hedges and dense copses. It was enough to make you want to burst into a chorus of 'There'll Always Be an England' except that neither of them felt like singing.

Why had she run? That was what Hester said she couldn't understand. Everything else seemed logical enough: how she would have got hold of the cryptograms in the first place, why she might have wanted to read them, why she would have needed an accomplice. But why then commit the one act guaranteed to draw attention to yourself? Why fail to turn up for your morning shift?

'You,' she said to Jericho, after she had thought it over for a few more miles. There was a hint of accusation in her voice. 'I think it must be you.'

Like a prosecuting counsel she took him back over the events of Saturday night. He had gone to the cottage, yes? He had discovered the intercepts, yes? A man had arrived downstairs, yes?

'Yes.'

'Did he see you?'

'No.'

'Did you say anything?'

'I may have shouted "Who's there?" or something of the sort.'

'So he could have recognised your voice?'

'It's possible.'

But that would mean I knew him, he thought. Or at least that he knew me.

'What time did you leave?'

'I don't know exactly. About half past one.'

'There you are,' she said. 'It is you. Claire returns to the cottage after you've gone. She discovers the intercepts are missing. She realises that you must have them because this mysterious man has told her you were there. She believes you'll take them straight to the authorities. She panics. She runs

'But that's madness.' He took his eyes off the road to stare at her. 'I'd never have betrayed her.'

'So you say. But did she know that?'

Did she know that? No, he realised, returning his attention to the wheel, no, she did not know that. Indeed, on the basis of his behaviour on the night she found the cheque, she had good reason to assume he was a fanatic about security – a pretty ironic conclusion, given he now had eleven stolen cryptograms stuffed inside his overcoat pocket.

A twenty-year-old bus with an outside staircase to its upper deck, like something out of a transport museum, pulled over to the grass verge to let them overtake. The schoolchildren on board waved frantically as they passed.

'Who were her boyfriends? Who was she seeing apart from me?'

'You don't want to know. Believe me? There was relish in the way she threw back at him the words he had used to her in church. He couldn't blame her for it.

'Come on, Hester.' He gripped the steering wheel grimly and glanced into the mirror. The bus was receding from view. A car was emerging from behind it. 'Don't spare my blushes. Let's keep it simple. Just confine it to men from the Park.'

Well, they were impressions, she said, rather than names. Claire had never mentioned names.

Give me the impressions, then.

And she did.

The first one she'd encountered had been young, with reddish hair, clean-shaven. She'd met him on the stairs with his shoes in his hand one morning in early November.

Reddish hair, clean-shaven, repeated Jericho. It didn't sound familiar.

A week later she'd cycled past a colonel parked in the lane in an Army staff car with the headlights dowsed. And then there was an Air Force man called Ivo Something, with a weird vocabulary of 'prangs' and 'crates' and 'shows' that Claire used to mimic fondly. Was he Hut 6 or 3? She was fairly sure Hut 3. There was an Honourable Evelyn double-barrelled someone-or-other – 'thoroughly dishonourable, darling' – whom Claire had met in London during the Blitz and who now worked in the mansion. There was an older man who Hester thought had something to do with the Navy. And there was an American: he was definitely Navy.

'That would be Kramer,' said Jericho.

'You know him?'

'He's the man who lent me the car. How recent was that?'

'About a month ago. But I got the impression he was just a friend. A source of Camels and nylons, nothing special.'

'And before Kramer there was me.'

'She never talked about you.'

'I'm flattered.'

'Given the way she used to talk about the others, you should be.'

'Anyone else?'

She hesitated. 'There may have been someone new in the last month. She was certainly away a good deal. And once, about two weeks ago, I had a migraine and came home early off shift and I thought there was a man's voice coming from her room. But if there was they stopped talking when they heard me on the stairs.'

'That's eight then, by my count. Including me. And leaving out any others you've forgotten or don't know about.'

'I'm sorry, Tom.'

'It's quite all right.' He managed to arrange his face into a parody of a smile. 'If anything it's rather fewer than I'd thought.' He was lying, of course, and he guessed she knew it. 'Why is it, I wonder, that I don't hate her for it?'

'Because that's the way she is,' said Hester, with unexpected ferocity. 'Well, she never made much secret of it, did she? And if one hates her for what she is – then, really, one can't have loved her very much in the first place, can one?' Her neck had blushed a deep pink. 'If all one wants is a reflection of oneself – well, honestly, there's always the mirror.'

She sat back, apparently as surprised by this speech as he was.

He checked the road behind them. Still empty apart from the same, solitary car. How long since he'd first noticed it? About ten minutes? But now he came to think of it, it had probably been there a good while longer, certainly since before they overtook the school bus. It was lying about a hundred yards back, low and wide and dark, its belly close to the ground, like a cockroach. He squeezed his foot harder on the accelerator and was relieved to see the gap between them widen until at last the road dipped and turned and the big car disappeared.

A minute later it was back again, maintaining exactly the same distance.

The narrow lane ran between high, dark hedges flecked with buds. Through them, as through a magic lantern, Jericho caught odd glimpses of tiny fields, a ruined barn, a bare, black elm, petrified by lightning. They came to a longish stretch of flat road.

There was no sun. He calculated there must be about half an hour of daylight left.

'How far is it to Bletchley?'

'Stony Stratford coming up, then about six miles. Why?'

He looked again in the mirror and had just begun to say, 'I fear -' when a bell started to clamour behind them. The big car had finally tired of following and was flashing its headlights, ordering them to pull over.

Until this moment, Jericho's encounters with the police had been rare, brief and invariably marked by those exaggerated displays of mutual respect customary between the guardians of the law and the lawful middle classes. But this one would be different, he saw that at once. An unauthorised journey between secret locations, without proof of ownership of the car, without petrol coupons, at a time when the country was being scoured for a missing woman: what would that earn them? A trip to the local police station, for sure. A lot of questions. A telephone call to Bletchley. A body search.

It didn't bear contemplating.

And so, to his astonishment, he found himself measuring the road ahead, like a long-jumper at the start of his run. The red roofs and the grey church spire of Stony Stratford had begun to poke above the distant line of trees.

Hester grabbed the edges of her seat. He jammed his foot down hard to the floor.

The Austin gathered speed slowly, as in a nightmare, and the police car, responding to the challenge, began to gain on them. The speedometer climbed past forty, to fifty, to fifty-five, to nearly sixty. The countryside seemed to be racing directly at them, only swerving at the last second to flash by narrowly on either side. A main road appeared ahead. They had to stop. And if Jericho had been an experienced driver that is what he would have done, police or no police. But he hesitated until there was nothing he could do but brake as hard as he dared, change down into second gear and yank the steering wheel hard left. The engine screamed. They spun and cornered on two tyres, he and Hester pitched sideways by the force. The clanging bell was drowned by the roar of an engine and suddenly the radiator grille of a tank transporter was rushing to fill the rear-view, mirror. Its bumper touched them. An outraged blast from its hooter, as loud as a foghorn, seemed to blow them forwards. They shot across the bridge over the Grand Union Canal and a swan turned lazily to watch them and then they were doglegging through the market town – right, left, right, shuddering over cobbled alleys, the wheel shaking in Jericho's hands – anything to get off this wretched Roman road. Abruptly the houses receded and they were out in open country again, running alongside the canal. A narrowboat was being towed by a weary carthorse. The bargeman, lying stretched out beside the tiller, raised his hat to them.

'Left here,' said Hester, and they swung away from the canal into a lane that was not much better than the forest track: just two strips of potholed, tarmaced road, extending ahead like tyre tracks, separated by a mound of grass that scraped the bottom of the car. Hester turned and knelt on her seat, staring out of the back window for any sign of the police, but the countryside had closed behind them like a jungle. Jericho drove on slowly for two miles. They passed through a tiny hamlet. A mile the other side of it a space had been dug out to allow cars – or, more likely, carts – to pass one another. He drove up into it and switched off the engine.

They did not have much time.

Jericho kept watch on the lane while she changed in the back seat of the Austin. According to the map, they were only about a mile due west of Shenley Brook End and she was insistent she could make it back to the cottage on foot across open country before dark. He marvelled at her nerve. To him, after the encounter with the police, everything had taken on a sinister aspect: the trees gesticulating at one another in the wind, the patches of dense shadow now gathering at the edges of the fields, the rooks that had erupted, cawing, from their nests and were now circling high above them.

'Can't we read them?' Hester had asked, after they had parked. He had taken the cryptograms from his pocket so that they could decide what to do with them. 'Come on, Tom. We can't just burn them. If she thought she could read them, why can't we?'

Oh, a dozen reasons, Hester. A hundred. But here were three to be going on with. First, they would need the Vulture settings that were in use on the days the signals were sent.

'I can try to get those,' she had said. 'They must be in Hut 6 somewhere.'

Very well, maybe she could. But even if she managed it, they would still need several hours to themselves on a Type-X machine – and not one of the Type-Xs in Hut 8, either, because naval Enigmas were wired differently from Army ones.

She had made no answer to that.

And, third, they would need to find a place to hide the cryptograms, because otherwise, if they were caught with them, they'd both be on trial in camera at the Old Bailey.

No answer to that, either.

There was a movement in the hedge about thirty yards ahead of him. A fox came nosing out of the undergrowth and stepped into the lane. Halfway across it stopped and stared directly at him. It held itself perfectly still and sniffed the air, then slouched off into the opposite hedgerow. Jericho let out his breath.

And yet, and yet… Even as he had ticked off all the obvious objections, he had known that she was right. They couldn't simply destroy the cryptograms now, not after all they had gone through to get them. And once that was conceded then the only logical reason for keeping them was to try to break them. Hester would have to steal the settings somehow while he looked for a way of gaining access to a Type-X machine. But it was dangerous – he prayed that she could see that. Claire was the last person to steal the cryptograms and there was no telling what had happened to her. And somewhere – maybe looking for them now, for all they knew – was a man who left large footprints in the frost; a man apparently armed with a stolen pistol; a man who knew that Jericho had been in Claire's room and had taken away the signals.

I am no hero, he thought. He was scared half to death.

The car door opened and Hester emerged, dressed again in trousers, sweater, jacket and boots. He took her bag and stowed it in the Austin's boot.

'Are you sure you don't want me to drive you?'

'We've been over this. It's safer if we split up.'

'For God's sake then be careful.'

'You should worry about yourself.' The air was milky with the approaching dusk – damp and cold. Her face was beginning to blur. She said: I'll see you tomorrow.'

She swung herself easily over the gate and set off directly across the field. He thought she might turn and wave but she never looked back. He watched her for about two minutes, until she had safely reached the far side. She searched briefly for a gap in the hedge, then vanished like the fox.

5

The lane led him up over the Chase, past the big wireless masts of the Bletchley Park out-station at Whaddon Hall, and down to the Buckingham Road. He peered along it, cautiously.

According to the map, only five roads, including this one, connected Bletchley with the outside world, and if the police were still watching the traffic they would stop him, he was certain. Short of flying a swastika the Austin could hardly have looked more suspicious. Mud was spattered over the bodywork to the height of the windows. Grass was wrapped tightly around the axles. The back bumper was buckled where the tank transporter had struck it. And the engine, after Stony Stratford, had acquired a kind of urgent death rattle. He wondered what on earth he would say to Kramer.

The road was quiet in both directions. He passed a couple of farmhouses and within five minutes he was entering the outskirts of the town. He drove on past the suburban villas with their white pebble-dashed frontages and their fake Tudor beams, then left up the hill towards Bletchley Park. He turned into Wilton Avenue and immediately braked. Parked at the end of the street beside the guard post was a police car. An officer in a greatcoat and cap was talking earnestly to the sentry.

Once again, Jericho had to use both hands to jam the gear lever into reverse, then he backed out very slowly into Church Green Road.

He had moved beyond panic now and was in some calm place at the centre of the storm. 'Act as normally as possible', that had been his advice to Hester when they had decided to keep the cryptograms. 'You're not on duty until four tomorrow afternoon? Fine, then don't go in before that time.' The injunction must apply to him as well. Normality. Routine. He was expected in Hut 8 for the night's attack on Shark? He would be there.

He drove on up the hill and parked the car in a street of private houses about three hundred yards from St Mary's Church. Where to hide the cryptograms? The Austin? Too risky. Albion Street? Too likely to be searched. A process of elimination brought him to the answer. Where better to hide a tree than in a forest? Where better to conceal a cryptogram than in a code-breaking centre? He would take them into the Park.

He transferred the wad of paper from the inside pocket of his overcoat to the hiding place he had made in the lining and locked the car. Then he remembered Atwood's atlas and unlocked it again. Bending to retrieve the book he casually checked the road. A woman in the house opposite was standing on her doorstep, in an oblong of yellow light, calling her children in from play. A young couple strolled past, arm in arm. A dog loped miserably along the gutter and stopped to cock its leg against the Austin's front tyre. An ordinary, English provincial street at twilight. The world for which we fight. He closed the door quietly. Head down, hands in pockets, he set off at a brisk walk for the Park.

It was a matter of pride with Hester Wallace that, when it came to walking, she had the stamina of any man. But what had looked on the map to be a straight and easy mile had turned into a crooked ramble three times as long, across tiny fields enclosed by tangled hedges and by ditches swollen wide as moats with brown meltwater, so that it was almost dark by the time she reached the lane.

She thought she might be lost but after a minute or two the narrow road began to seem familiar to her – a pair of elms grown too close together, as if from the same root; a mossy and broken stile – and soon she could smell the fires in the village. They were burning green wood and the smoke was white and acrid.

She kept a look out for policemen, but saw none – not in the field opposite the cottage, nor in the cottage itself, which had been left unlocked. She bolted the front door behind her, stood at the bottom of the stairs and called out a greeting.

Silence.

Slowly she climbed the stairs.

Claire's room was in chaos. Desecrated was the word that came to mind. The personality it had once reflected was disarranged, destroyed. Her clothes had all been strewn about, the sheets stripped off her bed, her jewellery scattered, her cosmetics opened up and spilled by clumsy male hands. At first she thought the surfaces were coated in talcum, but the fine white dust had no smell, and she realised it must be fingerprint powder.

She made a start at clearing it up, but soon abandoned it and sat on the edge of the naked mattress with her head in her hands until a great wave of self-disgust made her leap to her feet. She blew her nose angrily and went downstairs.

She lit a fire in the sitting room and set a kettle full of water on the hearth. In the kitchen she riddled the stove and managed to coax a glow from the pale ash, piled on some coal and set a saucepan to boil. She carried in the tin bath from the outhouse, bolting and locking the back door behind her.

She would stifle her terrors with routine. She would bathe. She would eat the remains of last night's carrot flan. She would retire early and hope for sleep.

Because tomorrow – tomorrow – would be a frightening day.

Inside Hut 8 there was a crowded, nervous atmosphere, like the green room of a theatre on opening night.

Jericho found his usual place next to the window. To his left: Atwood, leafing through Dilly Knox's edition of the mimes of Herodas. Pinker opposite, dressed as if for Covent Garden, his black velvet jacket slightly too long in the sleeve, so that his stubby fingers protruded like mole's paws. Kingcome and Proudfoot were playing with a pocket chess-set. Baxter was rolling a series of spindly cigarettes with a little tin contraption that didn't work properly. Puck had his feet up on the desk. The Type-Xs clacked sporadically in the background. Jericho nodded a general good evening, gave Atwood back his atlas – 'Thank you, dear boy. Good trip?' – and draped his overcoat over the back of his slatted chair. He was just in time.

'Gentlemen!' Logie appeared in the doorway and clapped twice to draw their attention, then stepped aside to allow Skynner to precede him into the room.

There was a general clatter and scraping of chair legs as they all clambered to their feet. Someone stuck their head round the door of the Decoding Room and the racket of the Type-Xs ceased.

'Easy, everybody,' said Skynner and waved them back into their seats. Jericho found that by tucking his feet under his chair he could rest his ankle against the stolen cryptograms. 'Just stopped by to wish you luck.' Skynner's heavy body was swathed like a Chicago gangster's in half an acre of pre-war, double-breasted pinstripe. 'I'm sure you're all aware of what's at stake here as well as I am.'

'Shut up, then,' whispered Atwood.

But Skynner didn't hear him. This was what he loved. He stood with his feet planted firmly apart, his hands clasped behind his back. He was Nelson before Trafalgar. He was Churchill in the Blitz. 'I don't think I'm exaggerating when I say this could be one of the most decisive nights of the war.' His gaze sought out each of them in turn, corning last of all to Jericho and sliding away with a flicker of distaste. 'A mighty battle – probably the greatest convoy battle of the war – is about to start. Lieutenant Cave?'

'According to the Admiralty,' said Cave, 'at nineteen hundred hours this evening, convoys HX-229 and SC-122 were both warned they had entered the presumed operational area of the U-boats.'

'There we are, then. "Out of this nettle, danger, may we pluck this flower, safety."' Skynner nodded abruptly. 'Go to it.'

'Haven't I heard that before somewhere?' said Baxter.

'Henry IV Part One.' Atwood yawned. 'Chamberlain quoted it before he went off to meet Herr Hitler.'

After Skynner had gone, Logie went round the room handing out copies of the convoy contact section of the Short Signal Code Book. To Jericho, as a mark of recognition, he gave the precious original.

'We're after convoy contact reports, gentlemen: as many of them as possible in the twenty-four hours between midnight tonight and midnight tomorrow – in other words, the maximum amount of crib covering one day's Enigma settings.'

The instant an E-bar signal was heard, the duty officer of the receiving station would telephone to alert them. When the contact report arrived by teleprinter a minute later, ten copies would be made and distributed. No fewer than twelve bombes – Logie had the personal guarantee of the Hut 6 bombe controller – would be placed at their disposal the moment they had a worthwhile menu to run.

As he finished his speech, the blackout shutters began to be fixed to the windows and the hut battened down for the night.

'So, Tom,' said Puck pleasantly. 'How many contact reports do you think we will need for this scheme of yours to succeed?'

Jericho was leafing through the Short Signal Code Book. He glanced up. 'I tried to work it out yesterday. I'd say about thirty.'

'Thirty?' repeated Pinker, his voice rising in horror. 'But that would m-m-mean a mmm-mmm-mmm -'

'Massacre?'

'Massacre. Yes.'

'How many U-boats would be needed to produce thirty signals?' asked Puck.

Jericho said: 'I don't know. That would depend on the time between the initial sighting and the start of the attack. Eight. Perhaps nine.'

'Nine,' muttered Kingcome. 'Christ! Your move, Jack.'

'Will someone tell me, then, please,' said Puck, 'for what I am supposed to be hoping? Am I hoping that the U-boats find these convoys or not?'

'Not,' said Pinker, looking round the table for support. 'Obviously. We w-w-want the convoys to escape the U-boats. That's what this is all about.'

Kingcome and Proudfoot nodded but Baxter shook his head violently. His cigarette disintegrated, sprinkling shreds of tobacco down the front of his cardigan. 'Damn it,' he said.

'You'd really s-s-sacrifice a c-c-convoy?' asked Pinker.

'Of course.' Baxter carefully brushed the loose tobacco into his palm. 'For the greater good. How many men has Stalin had to sacrifice so far? Five million? Ten million? The only reason we're still in the war is the butcher's bill on the eastern front. What's a convoy in comparison, if it gets us back into Shark?'

'What do you say, Tom?'

'I don't have an answer. I'm a mathematician, not a moral philosopher.'

'Bloody typical,' said Baxter.

'No, no, in terms of moral logic, Tom's is actually the only rational reply,' said Atwood. He had laid aside his Greek. This was the sort of discussion he liked. 'Consider. A madman seizes both your children at knife-point and says to you: "One must die, make your choice." Towards whom do you direct your reproaches? Towards yourself, for having to make a decision? No. Towards the madman, surely?'

Jericho said, staring at Puck: 'But that analogy doesn't answer Puck's point about what one should hope for.'

'Oh, but I would argue that that is precisely what it does answer, in that it rejects the premise of his question: the presumption that the onus is on us to make a moral choice. Quod erat demonstrandum.'

'Nobody can split a hair f-finer than F-Frank,' said Pinker, admiringly.

'"The presumption that the onus is on us to make a moral choice,"' repeated Puck. He smiled across the table at Jericho. 'How very Cambridge. Excuse me. I think I must visit the lavatory.'

He made his way towards the back of the hut. Kingcome and Proudfoot returned to their chess game. Atwood picked up Herodas. Baxter fiddled with his cigarette-rolling machine. Pinker closed his eyes. Jericho leafed through the Short Signal Code Book and thought of Claire.

Midnight came and went without a sound from the North Atlantic and the tension which had been building all evening began to slacken.

The 2 a.m. offering from the cooks of the Bletchley Park canteen was enough to make even Mrs Armstrong blanch – boiled potatoes in cheese sauce with barracuda, followed by a pudding made from two slices of bread stuck together with jam and then deep-fried in batter – and by four, the digestive effects of this, combined with the dim light in Hut 8 and the fumes from the paraffin heater, were casting a soporific pall over the naval cryptanalysts.

Atwood was the first to succumb. His mouth dropped open and the top plate of his dentures came loose so that he made a curious clicking sound as he breathed. Pinker wrinkled his nose in disgust and went off to make a nest for himself in the corner, and soon afterwards Puck, too, fell asleep, his body bent forwards, his left cheek resting on his forearms on the table. Even Jericho, despite his determination to stand guard over the cryptograms, found himself slipping over the edge of unconsciousness. He pulled himself back a couple of times, aware of Baxter watching him, but finally he couldn't fight it any longer and he slid into a turbulent dream of drowning men whose cries sounded in his ears like the wind in the aerial farm.