James is standing in a queue at Pret when his mobile rings. He's spent most of his lunch break on personal errands, and now has just enough time left to get a sandwich and a coffee to take back to the nick. Only this particular ringtone means a text from his governor. He glances at the screen, curses under his breath, and steps out of the queue. He's to meet Lewis in the Chief Super's office, ASAP.

As he strides down the pavement, his mind is busy with the puzzle of this unexpected summons. He doesn't think they've done anything recently that merits a bollocking. Their last case was a straightforward murder that did not involve the University or any of Oxford's elite. A new case? They shouldn't be due for one yet. Jake Husselbee was only arrested yesterday, and they've barely started on the follow-up interviews, let alone the paperwork.

Increasing his pace, he crosses Cornmarket, and is nearly run over by a cyclist riding illegally in the pedestrian zone. When he arrives at the nick, he takes a moment to compose himself. Whatever this is about, it won't be good for him to be snappish and out of sorts in a meeting with his governor and the Chief Super.

Innocent's admin waves him into her office. There's a man in one of the visitor chairs: clearly a copper, but one he doesn't recognise. Sharp suit, Italian shoes. Narrow face, piercing grey eyes that latch onto James as soon as he enters. Curiouser and curiouser. James greets Lewis with a respectful nod, then turns his attention to Innocent. "Ma'am?"

"Sergeant Hathaway." Innocent sounds relieved to see him, so it's most likely not a bollocking. "This is Detective Chief Inspector Archie Sutton from the Met. He's requested our assistance with a case involving multiple jurisdictions, now including Oxford."

Multiple jurisdictions? Have they got a serial killer here? James's mind is spinning as he seats himself in the vacant chair beside Lewis.

"I'm with the Art and Antiques Unit of the Met," Sutton begins. Art theft isn't usually associated with violence, so what does the Met want with a couple of murder detectives? "For the past 18 months, we've been tracking a seller of stolen antiquities. We haven't been able to determine if he is also the thief or if he's fronting for someone else."

In a roomful of senior officers, James hesitates to speak up, but as usual, Lewis's thoughts run parallel to his. "What sort of antiquities might those be?"

"They vary. A bronze French Empire mantel clock, woodblock prints from the Katsukawa school, a William III gold guinea, a 17th century astrolabe..." Sutton shrugs. "Something new every time. He approaches his buyers online, using some pretty sophisticated tricks to hide his tracks, or so the lads in computer forensics tell me."

"How does he identify potential buyers?" Innocent asks.

"We think he finds them on Internet forums for serious collectors. Most of the buyers we've spoken to are members of at least one. The descriptions of the suspect are different enough to each other that he must be using disguises. Facial hair, hair colour, even a tattoo on his neck once. He uses a new cover name for each sale, so we've taken to calling him the Fox."

"Sounds like a slick customer," Lewis says. "You've set traps for him, I suppose?"

"Oh, yes. He took the bait twice, but both times he scarpered at the last minute. Seems like he can smell a copper from a mile off. Now we've got him biting again. He asked for a meet tomorrow here in Oxford, though he hasn't revealed the location yet. We've got an officer with just the right background—public school, read art history at Cambridge, and best of all, he was a librarian before he joined the Met. This time, the stolen goods on offer are incunabula." Sutton pauses, a slight smile on his lips as he eyes Lewis.

Oh no, you don't. Before Lewis has to ask, James speaks up. "Early printed books produced prior to 1501. The term comes from the Latin word for cradle, because they are exemplars from the infancy of printing."

Lewis nods, unsurprised by his bagman's knowledge. Innocent looks pleased. Sutton is hard to read, but there's a hint of calculation in that shuttered face. The DCI reaches into his briefcase and retrieves a sheet of paper. "Sergeant Hathaway, would you please read this aloud?"

James looks at Innocent, who signals for him to go ahead. He looks at the paper. It's a printout from an online facsimile of a Latin incunable. The language is simple, especially compared to Augustine's De civitate dei. He clears his throat. "Quae se laudari gaudent verbis subdolis, serae dant poenas turpi paenitentia. Cum de fenestra corvus— It's Aesop. The fable of the fox and the raven. Erm... ma'am?"

Innocent hears the question he can't openly ask. "As I said, James, DCI Sutton needs our assistance with his case. The meeting is scheduled for tomorrow, and his officer has suddenly become... unavailable."

Sutton reddens. "He's got chickenpox, of all the bloody ridiculous things. Months of planning gone down the drain because Tom Winthorpe has gone spotty."

James takes a fleeting moment to feel pity for spotty Winthorpe, but only a moment, because he can see where this is going.

Lewis asks, "You can't stand in for him? Or another detective? I'd think a specialist unit like yours would have enough Oxbridge graduates in it to choke a horse."

"Not as many as you'd think. We rely on civilian consultants for a lot of the research aspects of the job. And the thing is, we've created a very specific persona for this meeting, all based on Winthorpe's background. We know from interviewing other buyers that the Fox is a chatty fellow. Likes to ask about the buyer's school, university, hobbies."

"Checking their bona fides."

"Exactly. There are plenty of officers in the Met and other services who are Cambridge graduates. When we narrow it down to the ones who are of the right age and can read Greek and Latin, it's a very short list. Five." He counts down the candidates and their disqualifications on the fingers on his right hand. "On holiday in New Zealand. Female. Heavy Welsh accent. And... not posh enough for the role."

"And what is that role?" candidate number five asks cautiously.

"Sir Edward Latham, Baronet."

Christ! Now he knows why Sutton has been giving him that cool, appraising stare. Pride wars with fear inside him. If he takes this on and blows it... what then? Innocent won't blame him; Lewis certainly won't. He'll just feel like a failure. No, he can't refuse. There's no one else who can take this on. If he bows out and they have to cancel the meeting, the Fox will be even more suspicious the next time—if there is a next time. James inhales, summoning the cocky mental armour of Wolfgang Christ, Head Boy. "Very well, Inspector. Shall we get started?"

Sutton looks pleased. "Right. Chief Superintendent Innocent has kindly given me an office to work in, so—"

"So we might as well go down to my office, since I'll be accompanying him," Lewis says.

"Hang on—you can't just insert yourself in my operation, willy-nilly!"

"You can't just commandeer my sergeant, and expect me to—"

"Gentlemen." Innocent raises her voice just enough to be heard. "Since Sergeant Hathaway is going to be the man on the spot, perhaps we should find out what he thinks. Sergeant?"

Another, deeper breath. James adopts the supercilious tone of the most annoying boy in the sixth form. "Naturally, Lewis will be driving me."

"So I'm your chauffeur, am I?" His governor sounds amused.

"Chauffeur, factotum, gardener..." James leans forward and murmurs to Sutton, "A bit rough around the edges, but utterly dependable."

Lewis snorts. Innocent coughs behind her hand. Sutton seems torn between amusement and indignation. "Very well, Sir Edward. Certainly, I wouldn't want to deprive you of your right hand man."

James sits at his desk, bent over the computer. Sutton has given him access to Winthorpe's account so he can read all the emails between Winthorpe and 'Hugo Challoner' (the Fox's current alias). He pays particular attention to the wording of Winthorpe's messages, to get a feeling for his use of language. It's not too different to his own.

Sutton hands him a thick stack of printouts: background information on incunabula from a collector's point of view. "Winthorpe highlighted the bits that you really should know. Just... swot up as much as you can, yeah?"

James is ready to snap out a retort to this slur on his academic abilities. He looks up at Sutton, and swallows his words. Sutton's jaw is tight, his forehead creased. "Not to worry, sir. I did a minor course in swotting at Cambridge."

As he turns his attention to the printouts, he hears Lewis murmur, "C'mon, Sutton. Let's leave him to swot in peace."

There's a glossary at the top of the stack. Some of the terms are familiar to him: quire and quarto, colophon and codex. One of his theology lecturers at Cambridge thought it was good for his students to appreciate what reading and study were like for pre-modern scholars, and assigned some of the course readings as printouts of illuminated manuscripts and incunabula. James admires the craftsmanship of the scribes and printers who believed that to beautify the words on the page was to glorify God. Still, he's always been more interested in the contents of books than their physical form.

There are photos of pages from incunabula in library collections all over Europe. Many of the book titles are in German, and James is pleased to discover that he can make out most of them. His trip to Berlin two years ago had left him feeling ignorant and frustrated; shortly after the case was over, he'd found an online course in basic German. His accent is a bit rubbish, though it's better than his recent attempts at conversational Mandarin.

Die vierundzwanzig goldenen Harfen. The Twenty-Four Golden Harps. Dialogus linguae et ventris. Dialogue of the Tongue and Stomach. Die Ordnung der Gesundheit. The Rule of Health. Infantia Salvatoris. The Infancy of our Saviour. Places and dates, names of printers, and technical details of printing presses. Mainz, Subiaco, Strassburg. Gutenberg, 1455; Mentelin, 1460; Sweynheym, 1465. Punch, matrix, platen. Tympan, coffin, frisket. After an hour of this, the words begin to dance and blur. He rubs his eyes.

Naturally, Lewis and Sutton choose that moment to return. "How's it going, Sergeant Hathaway?"

"Sirs... I'm sorry, but I need to take a short break. I didn't eat lunch today."

"We'll have something brought up," Sutton says promptly.

"No, he should go down to the canteen," Lewis says firmly. "He'll work all the better for taking a few minutes."

James rolls his shoulders and arches his back before rising. "I won't be long." There's not much to choose from in the canteen, but in his current state, a ham sandwich and a cup of coffee are ambrosia and nectar. He takes ten full minutes to drink the coffee slowly, then buys a second cup to bring up to the office.

The door is ajar, and voices flow out into the corridor. "You really think he can learn enough of it by tomorrow afternoon?"

James freezes. This isn't a conversation he wants to walk into.

"I know it." Lewis's Geordie accent is more pronounced than usual; a sure sign that he's annoyed. "When you were looking up coppers who graduated from Cambridge, did you happen to notice that Hathaway took a starred First? They don't give those out to just anyone."

James's brows shoot up. He hadn't realised that Lewis knew that about him. He certainly never told Lewis, though naturally his governor has access to his personnel file.

"In theology. You think the Fox is going to ask him questions about the Pearly Gates?"

"Doesn't matter if he read theology or botany. Point is, he's used to learning a lot of complicated stuff quickly. An' he's done it on the job, too."

"That's all well and good, but the real test will be passing himself off as a baronet."

Lewis laughs. "Don't be ridiculous, man. Hathaway went to a posh school. You've heard him talk. He can out-nob any nob. I've seen him do it more than once, smooth as a cat in cream." James holds his breath, but of course Lewis doesn't mention Crevecoeur. He's discreet, and keeps secrets without being asked.

"That's as may be," Sutton grumbles, "but it's not me he's got to convince, it's the Fox."

If you think so little of me, why did you ask me to play the role? James knows the answer: because Sutton has no better alternative. He doesn't much care what Sutton thinks of him, but he dreads disappointing Lewis.

The two inspectors fall silent. James retreats a few metres down the corridor, and then returns, walking briskly. As he enters the office, Lewis smiles. Sutton nods. "Sergeant Hathaway, leave off the reading for a while longer. I'd like to discuss the objectives and tactics for tomorrow's operation."

James bobs his head and seats himself at his desk.

Sutton begins his instruction with an overview of the laws concerning entrapment. He outlines different possible scenarios, and what James should say and do in each case. He writes the most important points on a whiteboard. James has to admit that Sutton knows what he's doing. He's annoying, but he's a good detective, and he knows the ins and outs of his specialty.

Lewis insists on ending the day at a normal hour. "You won't be at your best tomorrow if you wear yourself out reading and fretting. No, leave those here," he directs as James reaches for the stack of paperwork. "We'll see you in the morning," he says to Sutton.

Lewis drives James home, stopping en route for a Chinese takeaway. Fried wontons, Kung Po chicken, and a bottle of Tsingtao beer do a lot to relax him. A conversation about everything except work does even more. Lewis bids him good night after the News at Ten. "I'll pick you up at half-seven." He pauses. "Sleep well." It's more than a wish and less than an order.

"Good night, sir."

James sleeps, though not well. He dreams of books: huge books, large enough to crush him if they fall, bound in blood-red leather. The books open to reveal images hand-drawn in the margins of the printed pages. Drolleries and grotesques come to life and go skipping off the paper. There's a nun riding side-saddle on a mouse, and an archer jumping out of a flower bud to shoot at a bird-headed monkey. Demonic snails slither off the page. A fox with a flaming tail runs across the ceiling, only it's not a tail, it's a red silk banner embroidered in gold with one word: Versager. Failure.

You don't get away that easily! James springs up and pursues the fox around the room until it runs in front of one of the giant books. He grasps the cover with both hands and slams it shut, trapping the fox inside. Gotcha! There's an old-fashioned wire cage in his hand, about the size of a cat carrier. Cautiously, he opens the book again, ready to grab his prey.

The fox isn't there. The page is blank. Completely blank. No text, no drawings. Nothing. He turns to the next page. Blank. The next. Blank. Frantically, he flips pages faster and faster. Blank. Blank. Blank. Blankblank. Blankblankblankblank...

On the final page, a woodblock print of an elderly man gazes out at James. He's wearing a pointy hat trimmed with fur, and a pleated jacket with split oversleeves and a fur collar. His left hand holds a piece of movable type; his right hand strokes a long, narrow, two-stranded beard that comes down to mid-chest. James recognises the man from his study materials: Johannes Gutenberg.

Gutenberg opens his mouth to speak, and his words appear in a heavy Gothic font marching across the page. "Der Fuchs ist entfleucht!" The fox has escaped!

James clenches his fists. "Oh, that's helpful."

"Gehabt Euch wohl," Gutenberg replies. Fare thee well. His image on the page contracts into a shapeless blob of ink, growing smaller and smaller until it vanishes entirely.

The alarm rings all too soon. James dresses quickly and is waiting on the pavement when Lewis arrives. They say very little. Lewis pulls into a cafe on the way to the nick, and waits while James dashes in to get two coffees and a couple of croissants.

A minute after they arrive in the office, Sutton walks in without knocking. He nods at each of them in turn. "Lewis, Hathaway. Morning."

"Good morning, Inspector. What happens next?"

"If the Fox holds to pattern, he'll email us about the meeting place at the last minute. He'll have been there for at least an hour, so any attempts to insert plainclothes officers will be nearly impossible." Sutton glances at his watch. "Since he indicated an afternoon meeting, we've some time yet. Let me show you the car so you can familiarise yourselves with it."

Down in the car park, James can immediately spot where 'his' car must be by the crowd of junior officers clustered around it like bees swarming a slice of ripe melon. Sutton is frowning, though none of the officers are touching the vehicle, which James can now see is a brand new sporty Jaguar. It's metallic blue, and the registration plate indicates that it's from Berkshire, Sir Edward's county of residence. "Very nice."

Lewis raises his voice. "All right, lads. Showtime's over. Clear off." The coppers do as they're told, though some of them walk slowly, with wistful glances over their shoulders.

Sutton turns to Lewis. "Let's kill two birds with one stone. The clothing for you two is in my hotel room, and you should get some practice in driving this beast. I imagine it handles differently to what you're used to."

"I owned a Jag once," Lewis replies. "A Mark 2. Didn't have all of these electronic gadgets, just a radio and a tape player."

"Used to own a Jag?" Sutton repeats.

Lewis settles himself in the driver's seat. "Yeah, but I sold it, years ago. Wanted the money for me kids' educations." He beckons to James. "Hathaway, sit in the front and tell me what all the digital thingummies are."

James does as he's bid. He shows Lewis the essentials controls and displays. "In the unlikely event that Challoner gets into this car, I'll explain that I have a Luddite for a driver."

"Smartarse," Lewis grumbles. "Sutton, where are we going?"

"Hotel Royale. It's—"

"I know it."

The Hotel Royale doesn't entirely live up to its name. James imagines that the Met's travel budget doesn't cover the Randolph or the Royal Oxford. Still, the Royale is pleasant enough, and it has a private car park. Sutton leads them up to his room. He gestures at two garment bags and a small rolling suitcase. "Gentlemen, your clothing is here." James finds an elegant pewter grey suit from a Hong Kong tailor, a crisp white shirt from Howard's of Paris, and an Italian silk tie. The gleaming shoes are also Italian. Clearly, 'buy British' is not Sir Edward's motto. Once he's fully dressed, James is presented with a Baume-et-Mercier wristwatch that must be worth a couple of thousand pounds.

Sutton correctly interprets James's frown. "Not to worry, Sergeant. The watch is a fake. Customs seized a crate of them last month."

"And the Fox won't notice?"

Sutton shrugs. "He'll think you're rich or gullible or both. It's a win-win situation." He hands James a sleek smartphone that's been programmed with the email account for Sir Edward.

Lewis comes out of the loo, looking uncomfortable in a perfectly-fitting brown tweed suit. It's off-the-rack from some expensive department store. Paired with a cream-coloured shirt and a dark brown tie, he appears both respectable and forgettable. He looks James up and down, and grins. "Well, now. You look posh enough for the entire House of Lords."

James shakes his head. Too posh for the House of Lords is closer to the truth. He's seen enough British peers—at a distance—at school and university to know that, on non-formal occasions, most of them prefer clothing that's comfortable and understated. Sir Edward's attire would be judged pretentious in the exclusive gentlemen's clubs in London where the peers of the realm gather. "And you look very... appropriate, sir."

"I'm just happy not to be in one of those daft chauffeur's uniforms with the cap and all. Reckon I'd feel like a doorman at a fancy hotel." Lewis pulls a face.

Time passes slowly. James re-reads the list of stolen books that he may be offered today. He and Lewis practice their hand signals. Sutton unbends enough to talk about some of the more interesting cases he's worked, and Lewis returns the favour. Room service brings up tea and sandwiches.

At 12:17, James's smartphone begins to play Bach's Toccata and Fugue in D minor. "That's the ringtone for incoming email," Sutton says.

James snatches up the phone and taps the email icon. He reads the message aloud. "Please join me for drinks at the Silver Swan. Send photo first. Come alone. HC." He fumbles with the unfamiliar phone, searching for the camera controls, and snaps several pictures of himself.

Lewis is explaining the Silver Swan to Sutton. It's a fancy pub, right by the river, with a large beer garden. "Very popular because of the view. It'd be almost impossible to sneak up on someone there." He looks over his shoulder at James. "Get a move on, will you?"

"Sorry, sir. Just deciding which photo to send."

Sutton turns. "This isn't Internet dating. Challoner won't care if you're smiling or not."

It's not that, James wants to say. He doesn't care if he looks good in the photo (he never does). It may be foolish, even superstitious, but he can't help thinking that, if he appears confident, the meeting will go well. He selects the best photo: one in which his eyes are neither closed nor so wide open that he looks stoned. He taps 'send', and tucks the phone into his jacket pocket. "I'm ready."

It's clear that Sutton would like to accompany them downstairs, perhaps even follow them out to the car park and watch them drive away. It can't be easy to turn over his case to two detectives he only met yesterday. To his credit, he only goes as far as the hallway.

Once inside the lift, James leans back against the wall and closes his eyes.

"It'll be all right," Lewis says quietly. "Once you're there and talking to the bugger, you won't have time to be nervous."

"If you say so, sir."

"I do say so. And now... I think you need to start as you mean to go on."

The lift chimes, and the doors part. Right. Now. James straightens, inhaling deeply as he does so. He strides into the lobby. "Lewis, fetch the car. I've a luncheon engagement at the Silver Swan."

"Yes, sir. Right away."

They don't talk in the car. Lewis-his-driver has nothing to say about his employer's destination; Lewis-his-governor has already said everything that needs saying. James resists the temptation to mentally review any of the case material. Instead, he gazes out the windows, trying to see Oxford through Edward Latham's eyes.

The traffic isn't bad for a weekday afternoon, and before James knows it, the Jag is entering the car park of the Silver Swan. Lewis pulls up to the pathway leading to the beer garden. James gets out, then leans into the still-open door. "I may be some time. After you park the car, come down and have a pint."

"Thank you, sir. That's kind of you."

It's an unnecessary conversation. They've already decided what to do, and there's no one nearby to overhear them. Only... Sutton had emphasised what James already knew from other undercover assignments: "Once the op's begun, you are to be in character every bloody moment, whether you're with the suspect or all alone in the loo."

Sir Edward Latham shuts the door of his Jaguar and strides towards the Silver Swan.