The birds have been singing all day. They come and sit on the telephone wires outside our window like notes on a stave, a score for some bizarre musical. I don't know how much longer I can stand it.

It's the end of the season. There has been a frost already, and most of the things that were once green have surrendered themselves to the shades at the lower end of the spectrum in a wave of pinks and reds, russets and browns. You can imagine that the colors go all the way off into invisibility, becoming pure radiant heat, soft and gentle and cozy like the glow of a log fire on a winter's evening.

Nothing much seems to have changed here. The lawns still slope to the shingle; the hills, dark and stormy with heather, still shoulder out of the other side of the loch. The jetty is still here, just a jutting tongue of wood succumbing to entropy, pilings rotting and slick with weed and algae, wear and tear from plimsolled feet and careless canoeists accounting for the odd plank here and there that nobody bothers replacing. I think they're just tired of it, letting it scatter softly of its own accord.

Disorder, Hey once told me, is the natural state of things. We measure the passage of time by the amount of change we see around us: a tree is taller, a rock is a little more weathered, a person is a little more wrinkled …

Perhaps that's why the past seems closer here, sitting on the jetty watching the loch lap unhurriedly at the beach like an old man sucking a mint imperial. You can ignore the various abrasions of entropy, concentrate instead on the Big Picture, the picture in which only the colors change, in strict procession, to the long slow beat of the seasons. It could be any autumn, any year.…

"I've been meaning to ask. Why do they call you Monkey?"

Shit, the bitch has crept up on me again. How the hell does she do that? "I don't remember," I answer without looking at her. "It was a joke, I think."

A polite snort, behind me. "A joke."

"One of Hey's jokes. Some people have an odd sense of humor." I look over my shoulder. "How's yours?"

Standing there, in her tweedy jacket and hiking trousers, hair pulled back in a painful-looking chignon, she tips her head to one side and regards me as if I'm a museum exhibit. Which from her point of view I may well be. At least twenty-five years separate us, and as usual I am on the wrong side of the equation.

"He killed a man," she reminds me again.

"Fine. I'll come to the trial." Which is actually quite amusing, because we both know that there will be no trial. Benedict's masters—and, temporarily, mine—have no intention of seeing Hey in court. Apart from the fact that it would be a dreadful breach of security and they would sooner kill Hey than have him walk into a British court, they're only interested in the things he took with him on the day he walked out of their corporate safe house in Oxfordshire, the things he carries in his head, the truly wonderful and arcane talents he has been developing for them.

She has taken every opportunity, in the weeks we've been chasing Hey, to remind me of the murder. She wheels it out every couple of days, typically when I show signs of flagging. On one memorably miserable drizzly day in Lincolnshire, she mentioned it seven times in one morning. She is trying to estrange me from him. Your old friend killed a man, Monkey. With his bare hands, Monkey. Does that sound like your old friend, Monkey?

It's a little sad that she relies on this litany. She's trying to tell me that Hey has changed beyond recognition, that I owe him no loyalty. She doesn't seem to have realized that I already know all this. I haven't seen Hey for the past seven years; how do I know what he's like now? Only the hills and the loch stay the same.

It must have irked Benedict's masters no end that Hey refused to work in America—from what she's told me about him, that much never changed. They would have liked to have flown him to their secure facility two kilometers beneath the Arizona desert, where escape is theoretically impossible, but he told them he couldn't work properly in the States. A sense of place was very important to him, he said; he wasn't averse to visiting America, touring other research facilities, pressing the flesh, putting his twopence worth into various projects. He just wouldn't work there.

So, because people have a phenomenal tolerance towards the kind of genius which is absolutely guaranteed to make them immense amounts of money, they bought Grantbridge House just for Hey. They equipped it to his specifications, made it as secure as modern paranoia can make a large building, and for years Hey worked there quite contentedly, within sight of the White Horse at Uffington. He used to send me Christmas cards signed "The Prisoner of Zenda" and "Rudolph Hess."

Until, one day, he just walked out.

Oh yes, Benedict, and he killed a man. I haven't forgotten.

"You came here as children," she says, walking along the jetty until she's standing just behind me. Her feet make almost no sound at all on the creaky boards; it's like the trick the David Carradine character used to do in Kung Fu, walking along a sheet of rice paper without leaving a mark. Except Benedict can do it in walking boots. She does it to annoy me; she knows I can't stand being crept up on.

To hide my irritation, I turn back to the loch, remember canoeing across it one day, a mile to the other side and a mile back, a hot heavy band of fatigue across my shoulders from paddling, while Hey trod foolishly about in the shallows like some awkward wading bird, examining the chunky quartz pebbles at the water's edge. When they were wet they were milkily translucent. Later, when he explained to me how a quartz crystal could be induced to vibrate as the heart of a clock, they had dried out and become almost opaque.

"Is that why he came here?" Benedict presses gently. When she wants to be, she is a creature of almost surreal gentleness; her Carolingian accent softens and broadens. She doesn't fool me, though. "Is it because you came here when you were young? All those outward-bound holidays your school arranged?"

Instead of reminding her that we only have the slimmest evidence that Hey was here at all, I say, "Tigers always return to a place of remembered beauty," recalling—probably with no great accuracy—a line from an old Jack Lemmon movie. "It's how they catch them."

"Is that how you think of Hey? As a tiger?"

I put my head back and laugh. There is probably no place in Benedict's life for philosophy, or for dead film stars. I hear her sigh, and when she speaks again her voice is brittle. "I'm going to take the NES scanner up the hill a ways." I catch the tiny sounds of her moving away; a squeak of rotting planks, the dry snap of a piece of driftwood as she reaches the shingle. "I want you to come and help."

I stand up. She's lying, of course. We both know that, and we both stopped caring weeks ago. She doesn't want my help; she would be far happier doing it on her own. What she really wants is to have me where she can see me.

"You're going to get us arrested," I said.

"They won't know which one of us to chase," Hey told me, drizzle running from his tangerine fringe.

"Terrific. So they'll only arrest one of us. I feel better already."

He laughed. Comparatively late in life, Hey had decided to take care of his body. Four times a week, he took a bus up to a sports center in Haringey and strapped himself into any number of chrome-and-leather, spring-and-cable Inquisition machines, lifting weights and twisting his body in directions mine would not move in. He had run in both the London and Boston marathons, and turned in respectable times in each. And then some idiot had introduced him to acrobatics.

Which set us down, at five past seven on a wet London morning in March, outside the old Public Records Office on Lincoln's Inn Fields. From the corner where we stood, I could see homeless people in the bushes of the little park, emerging from piles of soggy cardboard, newspaper, and plastic bags. Walking here from Holborn station, one of them had tried to bum some money from us. Hey had smiled hugely and given him a fifty-thousand zloty note, which he had picked up on holiday in Poland the year before and which you could only change for Sterling in Poland. Hey would do and say anything for a joke. I was often surprised that he had so many friends. Quite frequently, I was surprised that I was his friend.

"If we don't do it right now, we'll never do it," he said, looking across the road at the gates of Lincoln's Inn.

"That's all right by me," I said, wiping spots of rain from the plain-glass spectacles he'd made me wear as a disguise. His own camouflage, perversely, consisted of a bright orange wig and a huge false beard. He said he wanted to be as conspicuous as possible. He said he wanted people to remember this.

"It might be all right by you," he said, taking my arm, "but you're coming with me." And he marched me across the road and through one of the pedestrian gates that led into Lincoln's Inn.

The moment we set foot inside the Inn, I froze. Tall terraced barristers' chambers formed a square around a big lawn planted with trees and flower beds. Hundreds of windows looked down on us. It was very quiet; I could hear pigeons' wings clapping as they landed on the grass, hear the kettle boiling in the porters' lodge behind us as somebody brewed his morning cup of tea. I smelled the rain in the air, cigarette smoke on the breeze.

"I can't do this," I said. "It's stupid."

He regarded me sadly from behind his cushion of fake hair. "Monkey," he said, "I'm disappointed with you." And for one moment of unspeakable bliss the tone of his voice told me he'd given up his mad idea.

Then he winked, gave me the same grin he'd given the down-and-out, turned away from me, and before I could open my mouth he had performed a perfect cartwheel along the pavement and sprung into a series of flickflacks.

My jaw dropped. I'd never really thought that he would go through with it. I just stood watching like an idiot as he backflipped away from me down the side of the square.

A shout from the porters' lodge broke the spell. I took off along the top of the square. I heard running feet behind me and didn't dare stop. As I reached the corner and skidded right I risked a glance across the grass and almost got myself caught.

He was still flickflacking down the opposite side of the square, scattering people off the pavement, and he was beautiful. There was no sense of effort. He looked like a force of Nature.

I was so struck by the image that, if the hand behind me hadn't slipped on the rain-damp leather of my jacket, I would have been caught. Lungs bursting, I put on a spurt and pulled away, heard someone swear and fall heavily in my wake.

Hey had already reached the gateway at the bottom left-hand corner of the square, bouncing lightly to a stop on the balls of his feet and watching my approach with an expression of gentle unconcern. I pounded past him, fell over as I burst through the gateway and out onto Carey Street, rolled to my feet, glasses going flying into the road.

He caught up with me in a few easy strides and side by side we ran down Bell Yard beside the Law Courts and out onto the Strand, Hey dumping wig and beard in a litter bin as we ran by towards Aldwych and the Underground.

After subsequently spending many years trying to get around London by Tube, I have never understood how he managed to time it so perfectly. He must even have taken into account the timing of the traffic lights; we arrived at Aldwych station just as the bell rang to signal an incoming train. We were the last two into the lift. He was barely breathing hard; I could barely breathe at all.

I managed to get my wind back enough, on the train to Holborn a couple of minutes later, to gasp, "They were chasing me, you bastard!"

He shrugged.

"You knew I'd hesitate," I said, "didn't you. You knew I'd hesitate and they'd chase me rather than you."

He smiled.

At Holborn we hopped on a Piccadilly Line train as far as King's Cross, and a brisk trot along the tunnels to St. Pancras brought us out to the main-line station just as the last few passengers were getting onto the 0745 to Nottingham. I just had enough time to retrieve my bag from the locker where I'd left it an hour and a half before and jog stiff-legged up the platform.

"Just tell me you didn't enjoy that," he said, shaking my hand.

"Don't ever drag me into anything like that again," I told him, closing the carriage door and leaning out of the window. "Never ever."

Then the train gave a jerk and Hey and the station sailed away backwards as I was carried out into the morning rain. At that point I would have been particularly happy never to see Hey again.

Lots of things have changed.

Just over a month ago, my old friend Hey, genius, acrobat, coconspirator in the first and only Lincoln's Inn Marathon, went absent without leave from the corporation which owns him. Festooned with electronic bafflers which lesser minds are still struggling to understand, he simply walked through one of the most sophisticated cybernetic security systems ever installed in a house in this country, and evaporated.

Of the ten or fifteen staff on duty at the house that evening, only one was actually privileged enough to witness the Master Magician accomplishing his vanishing act. And, according to Benedict, Hey killed him.

A lot of people were left looking very silly, and, as far as I can understand it, Benedict and I represent part of the effort to put things right. Of course, in this context right is a relative term.

We walk the hills above the village all afternoon, Benedict carrying the scanner and hoping to pick up the nuclear battery we know Hey had with him in Lincolnshire, but all she finds is ancient background from the granite all around us.

Emptying into the loch near the hotel is a little burn, a rushing little stream foaming over rocks. Further up the hillside the burn cuts its own channel in the floor of a little U-shaped valley that opens way above the tree line into a craggy-walled glen cupping a tiny lozenge-shaped lochan, a perfect, still, black mirror of the sheer rock walls all around it and the streaks of cloud far above.

At the head of the glen I sit on a damp hummock of grass and light a small cigar. Benedict gives me a disapproving glare, but I flash her my best grin and carry on smoking and she drifts off holding the scanner in front of her like a charm against some very old and particularly British evil. A small group of sheep grazing near the lochan sees her heading its way and bolts, off-white blobs floating across the lumpy ground.

Benedict is from South Carolina. I like to think that makes her a Carolingian; it's my little history-teacher joke. She says she was born on one of the Sea Islands. Her father was a shrimp fisherman until one of the first great algal blooms of the early 2000s wandered up from the Florida coast and poisoned all the shrimp.

After that, he sold what he owned of the island on which Benedict was born and relocated the family to Savannah, where he found a job in some nontechnical branch of component manufacture, retrained to navvy for what they were still calling the Sunrise Industries when I was a boy.

The day after Benedict's tenth birthday, eighteen months after or so after leaving the Sea Islands, one of her father's workmates tried to ask him a question and found the ex-shrimper dead at his bench. He'd been dead for at least forty minutes, and nobody had noticed.

Benedict told me all this early on, when she was still interested in establishing a rapport. But I'm not very good at the kind of rapport she wants, the kind that amounts to betrayal.

"We'll sweep another quadrant tomorrow." Good Christ, how long has she been standing there?

"I don't think he's still here," I say nonchalantly, as if I haven't just had the wits scared out of me. "If he was here in the first place."

"We'll sweep another quadrant tomorrow," she repeats, putting the scanner back into its fitted chamois cover. The scanner is just one of the things on this trip which have disappointed Benedict, myself being another. Properly calibrated, it should in theory be able to pick up the radiation from the remains of Sellafield, miles to the south and west, but Hey's battery is nowhere to be found.

The scanner looks just like one of Mr Spock's tricorders. When I mentioned this to Benedict all she did was look at me with an expression of gentle pity, the kind of look I always imagine nineteenth-century missionaries giving to South Sea Islanders. She's too young to remember the original Star Trek, of course. Too young to remember moving pictures in less than three dimensions, come to that. I shouldn't blame her.

I look at the sky and say, "Beam me up, Scotty."

"You're sick, Monkey," she says, shaking her head.

We follow the burn back down the valley towards the loch. There's a tree up here, near the tree line, that I noticed on our last ramble. I call it the Cancer Tree. It seems to be dying a long and dreadful death. Huge granular cankers the size of fists are clustered on the trunk in a nearly symmetrical pattern; it has almost no leaves, even allowing for the lateness of the season, and it seems to be shedding branches as well, because several have simply fallen off and splashed down into the burn. I pointed it out the first time I saw it, but Benedict only gave it a cursory glance and said something about pollution, said Oregon had been hit by it. I don't think Benedict likes trees. I'm not entirely sure she likes people. Certainly she doesn't like me.

Just beyond the Cancer Tree, Benedict catches her toe on a stone half-buried in the grass and goes flying. It looks as if she bumps her knee quite painfully, but I just stand where I am and stare impassively, hoping to make her angry. I haven't seen Benedict angry yet; it ought to be quite instructive.

All she does, however, is pick herself up and glare at me before stomping off down the hill path again. Or rather, she glares at the two-centimeter CD-ROM I wear, as my one concession to contemporary fashion, pinned to the breast-pocket flap of my combat jacket. I have not told her yet that the jacket is older than she is. I'm saving that for a special occasion.