I guess this is the end. I’m in no condition to attempt the climb down, and in any case I’m running out of air. The nearest emergency shelter is only five klicks away, but it might as well be on the far side of this little moon. I’m not expecting any kind of last-minute rescue, either. No one knows I’m here, my phone and the distress beacon are out, my emergency flares went with my utility belt, and I don’t think that the drones patrol this high. At least my legs have stopped hurting, although I can feel the throb of what’s left of my right hand through the painkiller’s haze, like the beat of distant war drums . . .

If you’re the person who found my body, I doubt that you’ll have time to listen to my last and only testament. You’ll be too busy calling for help, securing the area, and making sure that you or any of your companions don’t trample precious clues underfoot. I imagine instead that you’re an investigator or civil servant sitting in an office buried deep inside some great bureaucratic hive, listening to this out of duty before consigning it to the memory hole. You’ll know that my body was found near the top of the eastern wall of the great gash of Elliot Graben on Ariel, Uranus’s fourth-largest moon, but I don’t suppose you’ve ever visited the place, so I should give you an idea of what I can see.

I’m sitting with my pressure suit’s backpack firmly wedged against a huge block of dirty, rock-hard ice. A little way beyond my broken legs, a cliff drops straight down for about a kilometer to the bottom of the graben’s enormous trough. Its floor, resurfaced a couple of billion years ago by a flood of water-ice lava, is a level plain patched with enormous fields of semi-vacuum organisms. Orange and red, deep blacks, foxy umbers, bright yellows . . . they stretch away from me in every direction for as far as I can see, like the biggest quilt in the universe. This moon is so small and the graben is so wide that its western rim is below the horizon. Strings of suspensor lamps float high above the fields like a fleet of burning airships. There’s enough atmospheric pressure, twenty millibars of nitrogen and methane, to haze the view and give an indication of distance, of just how big this strange garden really is. It’s the prison farm, of course, and every square centimeter of it was constructed by the sweat of men and women convicted by the failure of their ideals, but none of that matters to me now. I’m beyond all that up here, higher than the suspensor lamps, tucked under the eaves of the vast roof of fullerene composite and transparent halflife polymer that tents the graben. If I twist my head I can glimpse one of the giant struts that anchor the roof. Beyond it, the big, blue-green globe of Uranus floats in the black sky. The gas giant’s south pole, capped with a brownish haze of photochemical smog, is pointed at the brilliant point of the sun, which hangs just above the western horizon.

Sunset’s three hours off. I won’t live long enough to see it. My legs are comfortably numb, but the throbbing in my hand is becoming more urgent, there’s a dull ache in my chest, and every breath is an effort. I wonder if I’ll live long enough to tell you my story . . .

All right. I’ve just taken another shot of painkiller. I had to override the suit to do it, it’s a lethal dose . . .

Christos, it still hurts. It hurts to laugh.

My name is Roy Bruce. It isn’t my real name. I have never had a real name. I suppose I had a number when I was decanted, but I don’t know what it was. My instructors called me Dave—but they called all of us Dave, a private joke they never bothered to explain. Later, just before the war began, I took the life of the man in whose image I had been made. I took his life, his name, his identity. And after the war was over, after I evaded recall and went on the run, I had several different names, one after the other. But Roy, Roy Bruce, that’s the name I’ve had longest. That’s the name you’ll find on the roster of guards. That’s the name you can bury me under.

My name is Roy Bruce, and I lived in Herschel City, Ariel, for eight and a half years. Lived. Already with the past tense . . .

My name is Roy Bruce. I’m a prison guard. The prison, TPA Facility 898, is a cluster of chambers—we call them blocks—buried in the eastern rim of Elliot Graben. Herschel City is twenty klicks beyond, a giant cylindrical shaft sunk into Ariel’s icy surface, its walls covered in a vertical, shaggy green forest that grows from numerous ledges and crevices. Public buildings and little parks jut out of the forest wall like bracket fungi; homes are built in and amongst the trees. Ariel’s just over a thousand kilometers in diameter and mostly ice; its gravity barely exists. The citizens of Herschel City are arboreal acrobats, swinging, climbing, sliding, flying up and down and roundabout on cableways and trapezes, nets and ropewalks.

It’s a good place to live.

I have a one-room treehouse. It’s not very big and plainly furnished, but you can sit on the porch of a morning, watch squirrel monkeys chase each other through the pines. I’m a member of Sweat Lodge #23. I breed singing crickets, have won several competitions with them. Mostly they’re hacked to sing fragments of Mozart, nothing fancy, but my line has good sustain and excellent timbre and pitch. I hope old Willy Gup keeps it going . . .

I like to hike too, and climb freestyle. I once soloed the Broken Book route in Prospero Chasma on Miranda, twenty kilometers up a vertical face, in fifteen hours. Nowhere near the record, but pretty good for someone with a terminal illness. I’ve already had various bouts of cancer, but retroviruses dealt with those easily enough. What’s killing me—what just lost the race to kill me—is a general systematic failure something like lupus. I couldn’t get any treatment for it, of course, because the doctors would find out who I really am. What I really was.

I suppose that I had a year or so left. Maybe two if I was really lucky.

It wasn’t much of a life, but it was all my own.

Uranus has some twenty-odd moons, mostly captured chunks of sooty ice a few dozen kilometers in diameter. Before the Quiet War, no more than a couple of hundred people lived out here. Rugged pioneer families, hermits, a few scientists, and some kind of Hindu sect that planted huge tracts of Umbriel’s sooty surface with slow-growing lichenous vacuum organisms. After the war, the Three Powers Alliance took over the science station on Ariel, renamed it Herschel City, and built its maximum security facility in the big graben close by. The various leaders and lynchpins of the revolution, who had already spent two years being interrogated at Tycho, on Earth’s Moon, were moved here to serve the rest of their life sentences of reeducation and moral realignment. At first, the place was run by the Brazilian Navy, but civilian contractors were brought in after Elliot Graben was tented and the vacuum organism farms were planted. Most were ex-Service people who had settled in the Outer System after the war. I was one of them.

I had learned how to create fake identities with convincing histories during my training: my latest incarnation easily passed the security check. For eight and half years, Roy Bruce, guard third class, cricket breeder, amateur freestyle climber, lived a quiet, anonymous life out on the fringe of the Solar System. And then two guards stumbled across the body of Goether Lyle, who had been the leader of the Senate of Athens, Tethys when, along with a dozen other city states in the Outer System, it had declared independence from Earth.

I’d known Goether slightly: an intense, serious man who’d been writing some kind of philosophical thesis in his spare time. His body was found in the middle of the main highway between the facility and the farms, spreadeagled and naked, spikes hammered through hands and feet. His genitals had been cut off and stuffed in his mouth; his tongue had been pulled through the slit in his throat. He was also frozen solid—the temperature out on the floor of the graben is around minus one hundred and fifty degrees Centigrade, balmy compared to the surface of Ariel, but still a lot colder than the inside of any domestic freezer, so cold that the carbon dioxide given off by certain strains of vacuum organisms precipitates out of the atmosphere like hoar frost. It took six hours to thaw out his body for the autopsy, which determined that the mutilations were postmortem. He’d been strangled, and then all the other stuff had been done to him.

I was more than thirty klicks away when Goether Lyle’s body was discovered, supervising a work party of ten prisoners, what we call a stick, that was harvesting a field of vacuum organisms. It’s important to keep the prisoners occupied, and stoop labor out in the fields or in the processing plants leaves them too tired to plan any serious mischief. Also, export of the high-grade biochemicals which the vacuum organisms cook from methane in the thin atmosphere helps to defray the enormous cost of running the facility. So I didn’t hear about the murder until I’d driven my stick back to its block at the end of the shift, and I didn’t learn all the gruesome details until later that evening, at the sweat lodge.

In the vestigial gravity of worldlets like Ariel, where you can drown in a shower and water tends to slosh about uncontrollably, sweat lodges, saunas, or Turkish-style hamams are ideal ways to keep clean. You bake in steam heat, sweat the dirt out of your pores, scrape it off your skin, and exchange gossip with your neighbors and friends. Even in a little company town like Herschel City, there are lodges catering for just about every sexual orientation and religious belief. My lodge, #23, is for unattached, agnostic heterosexual males. That evening, as usual, I was sitting with a dozen or so naked men of various ages and body types in eucalyptus-scented steam. We scraped at our skin with abrasive mitts or plastered green depilatory mud on ourselves, squirted the baking stones of the hearth with water to make more steam, and talked about the murder of Goether Lyle. Mustafa Sesler, who worked in the hospital, gave us all the grisly details. There was speculation about whether it was caused by a personal beef or a turf war between gangs. Someone made the inevitable joke about it being the most thorough suicide in the history of the prison. Someone else, my friend Willy Gup, asked me if I had any idea about it.

“You had the guy in your stick last year, Roy. He have any enemies you know of?”

I gave a noncommital answer. The mutilations described by Mustafa Sesler were straight out of my training in assassination, guerrilla tactics, and black propaganda. I was processing the awful possibility that Goether Lyle had been murdered by someone like me.

You must know by now what I am. That I am not really human. That I am a doppelganger designed by gene wizards, grown in a vat, decanted fully grown with a headful of hardwired talents and traits, trained up, and sent out to kill the person whose exact double I was, and replace him. I do not know how many doppelgangers, berserkers, suicide artists and other cloned subversives were deployed during the Quiet War, but I believe that our contribution was significant. My target was Sharwal Jah Sharja, a minor gene wizard who lived alone in the jungle in one of the tented crevasses of East of Eden, Ganymede, where he orchestrated the unceasing symphony of the city state’s closed loop ecosystem. After I took his place, I began a program of ecotage, significantly reducing the circulation of water vapor and increasing the atmospheric concentration of carbon dioxide and toxic trace gases. By the time the Quiet War kicked off, some four weeks later, the population of East of Eden was wearing breathing masks, the forests and parks were beginning to die, and most food animals and crops had died or were badly stricken, forcing the city to use biomass from vacuum organism farms to feed its citizens. A commando force of the Three Powers Alliance annexed East of Eden’s farms in the first few hours of the war, and after two weeks its starving citizens agreed terms of surrender.

I was supposed to turn myself in as soon as the city had been secured, but in the middle of the formal surrender, dead-ender fanatics assassinated half the Senate and attacked the occupying force. In the subsequent confusion, the tented crevasse where I had been living was blown open to vacuum, Sharwal Jah Sharja was posted as one of the casualties, and I took the opportunity to slip away. I have successfully hidden my true identity and lived incognito amongst ordinary human beings ever since.

Why did I disobey my orders? How did I slip the bonds of my hardwired drives and instincts? It’s quite simple. While I had been pretending to be Sharwal Jah Sharja, I had come to love life. I wanted to learn as much about it as I could in the brief span I’d been allotted by my designers. And so I adopted the identity of another casualty, and after the war was over and the Three Powers Alliance allowed trade and travel to resume, I left East of Eden and went out into the Solar System to see what I could see.

In all my wanderings I never met any others like me, but I did find a hint that at least one of my brothers and sisters of the vat had survived the war. All of us had been imprinted with a variety of coded messages covering a vast range of possibilities, and a year after going on the run I came across one of them in a little-used passageway between two chambers of the city of Xamba, Rhea.

To anyone else it was a meaningless scrawl; to me, it was like a flash of black lightning that branded an enciphered phone number itself on my brain. The walls of the passageway were thickly scribbled with graffiti, much of it pre-war. The message could have been left there last year or last week; it could have been a trap, left by agents hunting renegades like me. I didn’t have the nerve to find out. I went straight to the spaceport and bought a seat on a shuttle to Phoebe, the gateway port to the other moons of Saturn and the rest of the Outer System. Six months later, wearing the new identity of Roy Bruce, I became a guard at TPA Facility 898.

That’s why, almost nine years later, I couldn’t be certain that any of my brothers and sisters had survived, and I was able to convince myself that Goether Lyle had been the victim of the vicious internal politics of the prison, killed and mutilated by someone who knew about the black propaganda techniques in which we’d been trained. But that comforting fiction was blown apart the very next day, when another mutilated body was found.

The victim was a former senator of Baghdad, Enceladus, and a member of the prison gang that was intermittently at war with the gang to which Goether Lyle had belonged. A message written in blood on the ground next to the senator’s body implied that he’d been murdered by Goether Lyle’s cronies, but whoever had killed him must have done the deed in his cell some time between the evening count and the end of the night’s lockdown, spirited his body out of the facility without being detected, and left it within the field of view of a security camera which had been hacked to show a recorded loop instead of a live feed. Members of the rival gangs lived in different blocks, had chips implanted in their skulls which constantly monitored their movements, and were under lock-down all night. If the killer was a prisoner, he would have had to bribe more than a dozen guards; it was far more likely that the senator had been killed by one of the facility’s staff. And when I heard what had been done to the body, I was certain that it was the handiwork of one of my brothers or sisters. The senator had been blinded before he’d been strangled, and his lungs had been pulled through incisions in his back. It was a mutilation called the Blood Eagle, invented by the Vikings some two thousand years ago. I remembered the cold, patient voice of the instructor who had demonstrated it to us on a corpse.

Someone in the warden’s office reached the same conclusion. Posted at the top of our daily orders was an announcement that a specialist team was on its way to Ariel, and emergency security measures were put in place at the spaceport. That evening Willy Gup told the sweat lodge that the warden reckoned that it was possible that the two murders were the work of the kind of vat-grown assassin used in the Quiet War.

“So if you come across anything suspicious, don’t be tempted to do anything stupidly heroic, my brothers. Those things are smart and deadly and completely without any kind of human feeling. Be like me. Stay frosty, but hang back.”

I felt a loathsome chill crawl through me. I knew that if Willy and the others realized that one of ‘those things’ was sitting with them in the steamy heat of the lodge, they would fall on me at once and tear me limb from limb. And I knew that I couldn’t hang back, couldn’t let things run their course. No one would be able to leave Ariel for the duration of the emergency security measures, and the specialist team would search every square centimeter of the facility and Herschel City, check the records and DNA profile of every prisoner, member of staff, citizen and visitor, and release a myriad tiny drones designed to home in on anyone breathing out the combination of metabolic byproducts unique to our kind. The team would almost certainly uncover the assassin, but they would also unmask me.

Oh, I suppose that I could have hiked out to some remote location on the surface and hunkered down for the duration, but I had no idea how long the search would last. The only way I could be sure of evading it would be to force my pressure suit put me in deep hibernation for a month or two, and how would I explain my absence when I returned? And besides, I knew that I was dying. I was already taking dangerously large daily doses of steroids to relieve the swelling of my joints and inflammation of my connective tissue caused by my pseudo-lupus. Suspended animation would slow but not stop the progress of my disease. Suppose I never woke up?

I spent a long, bleak night considering my options. By the time the city had begun to increase its ambient light level and the members of the local troop of spider monkeys were beginning to hoot softly to each other in the trees outside my little cabin, I knew what I would have to do. I knew that I would have to find the assassin before the team arrived.

My resolve hardened when I started my shift a couple of hours later and learned that there had been two more murders, and a minor riot in the prison library.

I found it laughably easy to hack into the facility’s files: I had been trained well all those years ago, and the data system was old, and was easily fooled. I checked the dossiers of recently recruited staff but found nothing suspicious, and didn’t have any better luck when I examined the dossiers of friends and family of prisoners, their advocates, and traders and businesspeople currently staying in Herschel City. It was possible that I had missed something—no doubt the assassin’s cover story was every bit as good as the one that had served me so well for so long. But having more or less eliminated the obvious suspects, I had to consider the possibility that, just like me, the assassin had been hiding on Ariel ever since the war had ended. I had so much in common with my brothers and sisters that it would not be a wild coincidence if one of them had come to the same decision as I had, and had joined the staff of the prison. Perhaps he had finally gone insane, or perhaps the hardwired imperatives of his old mission had kicked in. Or perhaps, like me, he had discovered that he was coming to the end of his short life span, and had decided to have some fun.

In the short time before the specialist team arrived, it would be impossible to check thoroughly the records of over three thousand staff members. I had reached a dead end. I decided that I needed some advice.

Everyone in Herschel City and the prison was talking about the murders. During a casual conversation with Willy Gup, I found it easy enough to ask my old friend if he had any thoughts on how someone might go about uncovering the identity of the assassin.

“Anyone with any sense would keep well clear,” Willy said. “He’d keep his nose clean, he’d keep his stick in line, and he’d wait for the specialists.”

“Who won’t be here for a week. A full-scale war could have broken out by then.”

Willy admitted that I had a point. One of the original intake of guards, a veteran who’d served in one of the Navy supply ships during the Quiet War, he had led the team that put down the trouble in the library. Three prisoners had died and eighteen had been badly injured—one had gouged out the eyes of another with her thumbs—and the incident had left him subdued and thoughtful.

After studying me for a few moments, he said, “If it was me, I wouldn’t touch the files. I hear the warden is compiling a list of people who are poking around, looking for clues and so forth. He tolerates their nonsense because he desperately wants to put an end to the trouble as soon as he can, and he’ll be pretty damn happy if some hack does happen to uncover the assassin. But it isn’t likely, and when this thing is over you can bet he’s going to come down hard on all those amateur sleuths. And it’s possible the assassin is keeping tabs on the files too. Anyone who comes close to finding him could be in for a bad surprise. No, my brother, screwing around in the files is only going to get you into trouble.”

I knew then that Willy had a shrewd idea of what I was about. I also knew that the warden was the least of my worries. I said, as lightly as I could, “So what would you do?”

Willy didn’t answer straight away, but instead refilled his bulb from the jar of iced tea. We were sitting on the porch of his little shack, at the edge of a setback near the top of the city’s shaft. Banana plants and tree ferns screened it from its neighbors; the vertical forest dropped away on either side. Willy’s champion cricket, a splendid white and bronze specimen in a cage of plaited bamboo, was trilling one of Bach’s Goldberg Variations. Willy passed the jar to me and said, “We’re speaking purely hypothetically.”

“Of course.”

“You’ve always had a wild streak,” Willy said, “I wouldn’t put it past you to do something recklessly brave and dangerously stupid.”

“I’m just an ordinary hack,” I said.

“Who goes for long solitary hikes across the surface. Who soloed that route in Prospero Chasma and didn’t bother to mention it until someone found out a couple of years later. I’ve known you almost nine years, Roy, and you’re still a man of mystery,” Willy said, and smiled. “Hey, what’s that look for? All I’m saying is you have character, is all.”

For a moment, my hardwired reflexes had kicked in. For a moment, I had been considering whether or not this man had blown my cover, whether or not I should kill him. I carefully manufactured a smile, and said that I hadn’t realized that I seemed so odd.

“Most of us have secrets,” Willy said. “That’s why we’re out here, my brother. We’re just as much prisoners as anyone in our sticks. They don’t know it, but those dumbasses blundering about in the files are trying to find a way of escaping what they are.”

“And there’s no way you can escape what you are,” I said. The moment had passed. My smile was a real smile now, not a mask I’d put on to hide what I really was.

Willy toasted me with his bulb of tea. “Anyone with any sense learns that eventually.”

“You still haven’t told me how you would catch the assassin.”

“I don’t intend to catch him.”

“But speaking hypothetically . . . ”

“For all we know, it’s the warden. He can go anywhere and everywhere, and he has access to all the security systems too.”

“The warden? Really?”

Willy grinned. “I’m pulling your chain. But seriously, I’ve done a little research about these things. They’re not only stone killers: they’re also real good at disguising themselves. The assassin could be any one of us. The warden, you, me, anyone. Unless this thing makes a mistake, we haven’t got a hope of catching it. All we can do is what we’re already doing—deploy more security drones, keep the prisoners locked down when they aren’t working, and pray that that’ll keep a lid on any unrest until that team arrives.”

“I guess you’re right,” I said.

“Don’t try to be a hero, my brother. Not even hypothetically.”

“Absolutely not,” I said.

But one of Willy’s remarks had given me an idea about how to reach out to the assassin, and my mind was already racing, grappling with what I had to do.

I decided that if the assassin really was keeping an eye on the people who were hacking into the files, then he (or at least, his demon), must be lurking in the root directory of the data system. That was where I left an encrypted message explaining what I was and why I wanted to talk, attached to a demon that would attempt to trace anyone who looked at it. The demon phoned me six hours later, in the middle of the night. Someone had spotted my sign and wanted to talk.

The demon had failed to identify the person who wanted to talk, and it was infected with something, too: a simple communication program. I checked it out, excised a few lines of code that would have revealed my location, and fired it up. It connected me to a blank, two-dimensional space in which words began to appear, emerging letter by letter, traveling from right to left and fading away.

>>you got rid of the trace function. pretty good for an old guy—if that’s what you really are.

>they trained us well, I typed.

>>you think you know what i am. you think that i am like you.

Whoever was at the other end of the program wanted to get straight down to business. That suited me, but I knew that I couldn’t let him take the lead.

>we are both children of the vat, I typed. that’s why I reached out to you. that’s why i want to help you.

There was a pause as my correspondent thought this over.

>>you could be a trap.

>the message got your attention because it is hardwired into your visual cortex, just as it is hardwired into mine.

>>that kind of thing is no longer the secret it once was, but let’s say that i believe you . . .

A black disc spun in the blank space for less than a second, its strobing black light flashing a string of letters and numbers, gone.

>>do you know where that is?

I realized that the letters and numbers burnt into my brain were a grid reference.

>i can find it.

>>meet me in four hours. i have a little business to take care of first.

It was the middle of the night; the time when the assassin did his work.

>please don’t kill anyone else until we have talked.

My words faded. There was no reply.

The grid reference was at the precise center of a small eroded crater sixty klicks south of the facility, an unreconstructed area in the shadow of the graben’s eastern rimwall. Before I headed out, I equipped myself from the armory and downloaded a hack into the security system so that I could move freely and unremarked. I was oddly happy, foolishly confident. It felt good to be in action again. My head was filled with a fat, contented hum as I drove a tricycle cart along an old construction road. The rendezvous point was about an hour away: I would have plenty of time to familiarize myself with the terrain and make my preparations before the assassin, if that was who I had been talking to, turned up.

I want to make it clear that my actions were in no way altruistic. The only life I wanted to save was my own. Yes, I knew that I was dying, but no one loves life more than those who have only a little of it left; no one else experiences each and every moment with such vivid immediacy. I didn’t intend to throw away my life in a grand gesture. I wanted to unmask the assassin and escape the special team’s inquisition.

The road ran across a flat terrain blanketed in vacuum-cemented grey-brown dust and littered with big blocks which over the eons had been eroded into soft shapes by impact cratering. The graben’s wall reared up to my left, its intricate folds and bulges like a frozen curtain. Steep cones and rounded hills of mass-wasted talus fringed its base. To my right, the land sloped away toward a glittering ribbon of fences and dykes more than a kilometer away, the boundary of the huge patchwork of fields. It was two in the morning by the clock, but the suspensor lamps were burning as brightly as they always did, and above the western horizon the sun’s dim spark was almost lost in their hazy glow.

I was a couple of klicks from the rendezvous, and the road was cutting through a steep ridge that buttressed a great bulge in the wall, when the assassin struck. I glimpsed a hitch of movement high in a corner of my vision, but before I could react, a taser dart struck my cart and shorted its motor. A second later, a net slammed into me, slithering over my torso as muscular threads of myoelectric plastic tightened in constricting folds around my arms and chest. I struggled to free myself as the cart piddled to a halt, but my arms were pinned to my sides by the net and I couldn’t even unfasten the safety harness. I could only sit and watch as a figure in a black pressure suit descended the steep side of the ridge in two huge bounds, reached me in two more. It ripped out my phone, stripped away my utility belt, the gun in the pocket on the right thigh of my pressure suit and the knife in the pocket on the left thigh, then uncoupled my main air supply, punched the release of my harness and dragged me out of the low-slung seat and hauled me off the road. I was dumped on my back near a cart parked in the shadow of a house-sized block and the assassin stepped back, aiming a rail-gun at me.

The neutron camera I’d fitted inside my helmet revealed scant details of the face behind the gold-filmed mirror of my captor’s visor. Its demon made an extrapolation, searched the database I’d loaded, found a match. Debra Thorn, employed as a paramedic in the facility’s infirmary for the past two years, 22, unmarried, no children . . . I realized then that I’d made a serious mistake. The assassin was a doppelganger, all right, but because she was the double of someone who hadn’t been an adult when the war had ended she must have been manufactured and decanted much more recently than me. She wasn’t insane, and she hadn’t spent years under cover. She was killing people because that was what she’d been sent here to do. Because it was her mission.

A light was winking on my head-up display—the emergency short-range, line-of-sight walkie-talkie. When I responded, an electronically distorted voice said, “Are you alone?”

“Absolutely.”

“Who are you?”

I’d stripped all identifying tags from my suit before setting off, but the doppelganger who had killed Debra Thorn and taken her place was pointing a gun at my head and it seemed advisable to tell her my name. She was silent for a moment, no doubt taking a look at my file. I said, “I’m not the doppelganger of Roy Bruce, if that’s what you’re thinking. The person I killed and replaced was a gene wizard by the name of Sharwal Jah Sharja.”

I briefly told the assassin the story I have already told you. When I was finished, she said, “You’ve really been working here for eight years?”

“Eight and a half.” I had made a very bad mistake about my captor’s motives, but I must have piqued her curiosity, for otherwise I would already be dead. And even if I couldn’t talk my way out of this and persuade her to spare me, I still had a couple of weapons she hadn’t found. I risked a lie, said that her net had compromised my suit’s thermal integrity. I told her that I was losing heat to the frozen ground, that I would freeze to death if I didn’t get up.

She told me I could sit up, and to do it slowly.

As I got my feet under me, squatting on my haunches in front of her, I glanced up at the top of the ridge and made a crucial triangulation.

She said, “My instructors told me that I would live no more than a year.”

“Perhaps they told you that you would burn briefly but very brightly—that’s what they told me. But they lied. I expect they lied about a lot of things, but I promise to tell you only the truth. We can leave here, and go anywhere we want to.”

“I have a job to finish.”

“People to kill, riots to start.”

The assassin took a long step sideways to the cart, took something the size of a basketball from the net behind its seat, bowled it towards me. It bounced slowly over the dusty ground and ended up between my legs: the severed head of an old woman, skin burnt black with cold, eyes capped by frost.

“The former leader of the parliament of Sparta, Tethys,” the assassin said. “I left the body pinned to the ground in one of the fields where her friends work, with an amusing little message.”

“You are trying to start a war amongst the prisoners. Perhaps the people who sent you here are hoping that the scandal will close the facility. Perhaps they think it is the only chance they’ll have of freeing their comrades. Who are you working for, by the way?”

“I’ll ask the questions,” the assassin said.

I asked her how she would escape when she was finished. “There’s a special team on the way. If you’re still here when they arrive, they’ll hunt you down and kill you.”

“So that’s why you came after me. You were frightened that this team would find you while they were hunting me.”

She may have been young, but she was smart and quick.

I said, “I came because I wanted to talk to you. Because you’re like me.”

“Because after all these years of living amongst humans, you miss your own kind, is that it?”

Despite the electronic distortion, I could hear the sneer in the assassin’s voice. I said carefully, “The people who sent you here—the people who made you—have no plans to extract you when you are finished here. They do not care if you survive your mission. They only care that it is successful. Why give your loyalty to people who consider you expendable? To people who lied to you? You have many years of life ahead of you, and it isn’t as hard to disobey your orders as you might think. You’ve already disobeyed them, in fact, when you reached out to me. All you have to do is take one more step, and let me help you. If we work together, we’ll survive this. We’ll find a way to escape.”

“You think you’re human. You’re not. You’re exactly like me. A walking dead man. That’s what our instructors called us, by the way: the dead. Not ‘Dave’. Not anything cute. When we were being moved from one place to another, they’d shout out a warning: ‘Dead men walking.’”

It is the traditional warning when a condemned person is let out of their cell. Fortunately, I’ve never worked in Block H, where prisoners who have murdered or tried to murder fellow inmates or guards await execution, so I’ve never heard or had to use it.

The assassin said, “They’re right, aren’t they? We’re made things, so how can we be properly alive?”

“I’ve lived a more or less ordinary life for ten years. If you give this up and come with me, I’ll show you how.”

“You stole a life, just as I did. Underneath your disguise, you’re a dead man, just like me.”

“The life I live now is my own, not anyone else’s,” I said. “Give up what you are doing, and I’ll show you what I mean.”

“You’re a dead man,” the assassin said. “You’re breathing the last of your air. You have less than an hour left. I’ll leave you to die here, finish my work, and escape in the confusion. After that, I’m supposed to be picked up, but now I think I’ll pass on that. There must be plenty of people out there who need my skills. I’ll work for anyone who wants some killing done, and earn plenty of money.”

“It’s a nice dream,” I said, “but it will never come true.”

“Why shouldn’t I profit from what I was made to do?”

“I’ve lived amongst people for more than a decade. Perhaps I don’t know them as well as I should, but I do know that they are very afraid of us. Not because we’re different, but because we’re so very much like a part of them they don’t want to acknowledge. Because we’re the dark side of their nature. I’ve survived this long only because I have been very careful to hide what I really am. I can teach you how to do that, if you’ll let me.”

“It doesn’t sound like much of a life to me,” the assassin said.

“Don’t you like being Debra Thorn?” I said.

And at the same moment I kicked off the ground, hoping that by revealing that I knew who she was I’d distracted and confused her, and won a moment’s grace.

In Ariel’s microgravity, my standing jump took me high above the assassin’s head, up and over the edge of the ridge. As I flew up, I discharged the taser dart I’d sewn into the palm of one of my pressure suit’s gloves, and the electrical charge stored in its super-conducting loop shorted out every thread of myoelectric plastic that bound my arms. I shrugged off the net as I came down and kicked off again, bounding along the ridge in headlong flight towards the bulging face of the cliff wall and a narrow chimney pinched between two folds of black, rock-hard ice.

I was halfway there when a kinetic round struck my left leg with tremendous force and broke my thigh. I tumbled headlong, caught hold a low pinnacle just before I went over the edge of the ridge. The assassin’s triumphant shout was a blare of electronic noise in my ears; because she was using the line-of-sight walkie-talkie I knew that she was almost on me. I pushed up at once and scuttled towards the chimney like a crippled ape. I had almost reached my goal when a second kinetic round shattered my right knee. My suit was ruptured at the point of impact and I felt a freezing pain as the smart fabric constricted as tightly as a tourniquet, but I was not finished. The impact of the kinetic round had knocked me head over heels into a field of ice-blocks, within striking distance of the chimney. As I half-crawled, half-swam towards it, a third round took off the top of a pitted block that might have fallen from the cliffs a billion years ago, and then I was inside the chimney, and started to climb.

The assassin had no experience of freestyle climbing. Despite my injuries I soon outdistanced her. The chimney gave out after half a kilometer, and I had no choice but to continue to climb the naked iceface. Less than a minute later, the assassin reached the end of the chimney and fired a kinetic round that smashed into the cliff a little way above me. I flattened against the iceface as a huge chunk dropped past me with dreamy slowness, then powered straight through the expanding cloud of debris, pebbles and ice grains briefly rattling on my helmet, and flopped over the edge of a narrow setback.

My left leg bent in the middle of my thigh and hurt horribly; my right leg was numb below the knee, and a thick crust of blood had frozen solid at the joint. But I had no time to tend my wounds. I sat up and ripped out the hose of the water recycling system as the assassin shot above the edge of the cliff in a graceful arc, taser in one hand, rail gun in the other. I twisted the valve, hit her with a high-pressure spray of water that struck her visor and instantly froze. I pushed off the ground with both hands (a kinetic round slammed into the dusty ice where I’d just been), collided with her in midair, clamped my glove over the diagnostic port of her backpack, and discharged my second taser dart.

The dart shorted out the electronics in the assassin’s suit, and enough current passed through the port to briefly stun her. I pushed her away as we dropped towards the setback, but she managed to fire a last shot as she spun into the void beyond the edge of the setback. She was either phenomenally lucky or incredibly skillful: it took off my thumb and three fingers of my right hand.

She fell more than a kilometer. Even in the low gravity, it was more than enough to kill her, but just to make sure I dropped several blocks of ice onto her. The third smashed her visor. You’ll find her body, if you haven’t already, more or less directly below the spot where you found mine.

The assassin had vented most of my air supply and taken my phone and emergency beacon; the dart I’d used on her had crippled what was left of my pressure suit’s life support system. The suit’s insulation is pretty good, but I’m beginning to feel the bite of the cold now, my hand is growing pretty tired from using the squeeze pump to push air through the rebreather, and I’m getting a bad headache as the carbon dioxide concentration in my air supply inexorably rises. I killed the ecosystem of East of Eden by sabotaging the balance of its atmospheric gases, and now the same imbalance is killing me.

Just about the only thing still working is the stupid little chip I stuck in my helmet to record my conversation with the assassin. By now, you probably know more about her than I do. Perhaps you even know who sent her here.

I don’t have much time left. Perhaps it’s because the increasing carbon dioxide level is making me comfortably stupid, but I find that I don’t mind dying. I told you that I confronted the assassin to save myself. I think now that I may have been wrong about that. I may have gone on the run after the Quiet War, but in my own way I have served you right up until the end of my life.

I’m going to sign off now. I want to spend my last moments remembering my freestyle climb up those twenty kilometers of sheer ice in Prospero Chasma. I want to remember how at the end I stood tired and alone at the top of a world-cleaving fault left over from a shattering collision four billion years ago, with Uranus tilted at the horizon, half-full, serene and remote, and the infinite black, starry sky above. I felt so utterly insignificant then, and yet so happy, too, without a single regret for anything at all in my silly little life.

First published in Asimov's Science Fiction, March 2006.