"It was a fiendish plan," said Mr Waverly, drawing at his pipe. "One might even say diabolical." A wisp of smoke rose like a ghost towards the ceiling, to be whisked away by the ventilation system. "To coerce people into working for Thrush by conditioning them to kill themselves if they disobeyed an order - and to kill themselves in the worst way they can imagine – well, it's the stuff of nightmares." He took the pipe out of his mouth and knocked it thoughtfully against the table top. "You were lucky they had no time to carry out the full programming on you, Mr Kuryakin. Very lucky indeed."

Napoleon's eyes started to slide in Illya's direction, but he stopped them in time. Illya wouldn't thank him for an indication of concern, no matter how minute. Besides, he didn't want Waverly to pick up on his reservations about Illya's report. Not yet, anyway. Not till he'd had a chance to talk to Illya himself.

He suspected Waverly had his own reservations. He was puffing away too placidly for his tranquility to be real, his attention apparently absorbed by the pipe, with only a fraction to spare for the two men sitting at the table opposite him.

"Medical tells me there is no trace of conditioning left," the Old Man went on, "so there's no risk of your attempting to assassinate Mr Solo the moment my back is turned." He exhaled another phantom breath. "That being the case, I suggest you two take the evening off. I imagine you have a certain amount to talk about, hmmm?"

Illya opened his mouth, possibly to protest, though it was hard to tell behind the blank mask he'd been cultivating ever since they got back from the island. Mr Waverly was taking no chances. The shaggy eyebrows drew together and a gale force glare blew away any objections Illya might have contemplated uttering.

"Yes, sir," said Napoleon, for both of them.

It might have been easier to obey Waverly's unspoken order in the open air. A park bench, perhaps - the classic setting for a cautious exchange of information between spies - or a walk under the trees, shuffling up leaves, with no obligation to look each other in the face. But it was the end of October, and darkness was already falling. They would have to go indoors, where the walls pressed too close, and faces pressed close, too. Napoleon suggested the name of a bar neither of them had been to before. It was near enough to walk to, and it was neutral territory.

Illya's face sported the glum expression he always wore when he was unhappy with an order but unwilling to disobey outright. At Napoleon's suggestion, he merely shrugged and fell into step beside him, brandishing his silence like a weapon. There was less than a foot between them, but when Illya withdrew into himself like this, it felt like the Grand Canyon.

Napoleon wondered where the hell he was even going to start. It was hard enough extracting information about himself from Illya at the best of times, and this wasn't exactly the best of times. In fact, it bore about as much resemblance to the best of times as a pile of dog crap bears to a gourmet meal. Come to think of it, chewed up and shat out was very much how Illya must be feeling. Napoleon sympathised. If he'd had some Thrush madman rummaging around inside his head, he wouldn't have wanted to talk about it, either.

He was going to have to try, though. Not just because Waverly wanted him to, but because he wanted to. Because of Illya's report. Because that goddamn laboratory had given him, Napoleon Solo, UNCLE's top agent, the kind of nightmares that only little kids and psychiatric patients suffer from. He had woken up sweating, his heart drilling through his chest, unable to believe at first that he was alive and undamaged. And that was without any conditioning.

How far was someone who had been through that programming still capable of functioning? Section 2 agents spent their lives on a cliff edge, death lunging for them from the abyss beneath. To keep your balance, you had to believe it wouldn't reach you. Couldn't reach you. If Partridge had made Illya live through his own death, in all its pain and blood and despair, how could he sustain that belief in his own immortality?

But they hadn't got that far. Not according to Illya's report.

"Hey, Illya, what did they really do to you in that lab?"

Yeah, like that would work. Whatever monsters might be crawling around Illya's psyche, he wasn't going to discuss them willingly. Napoleon would have to find a way to sneak up on the subject.

"Hey, Illya, would you really have..."

That had been part of the nightmares, too. Of course it had. It's not often your own partner tries to shoot your head off. It's not often you have to decide whether to shoot him back. Illya had snapped out of it in time, of course. But supposing he hadn't...

Napoleon squished the thought.

Instead he said, "Gee, I'd forgotten it was Halloween."

It was true, he had forgotten. Only that morning he'd flown in from a tropical paradise, where the wind sighed softly in breezy palm trees and the sea sparkled under a lazy sun. Now the sidewalk beneath his feet was slippery with wet leaves and the air was black and cold. And there were monsters everywhere.

There were cowboys and princesses and supermen among them, of course, but it was the manifestations of evil that caught Napoleon's eye. A werewolf with a shaggy head and a costume that appeared to have been stitched together out of dead Yorkshire terriers. A pale-faced vampire in a black cloak, whose teeth kept falling out. A miniature zombie, barely more than knee-high, with a luminous green face and bloody lips. As they passed, the zombie stretched out its skinny arms and said, "Rrrargh! Twick or tweat, mister!"

Napoleon laughed.

"Rrrargh," said the zombie, again. "Ain't you scared?"

"Terrified," said Napoleon, diplomatically.

"Well, gimme some candy, then!"

Napoleon found half a packet of rather elderly mints in one pocket, a legacy of the surveillance op he'd been on the last time he'd worn this coat. He gave the zombie a handful, and it skipped off down the road, still emitting enthusiastic Rrrraghs and Oaaarrrrs.

Napoleon looked over at Illya, who had his hands thrust deep in his coat pockets and was staring at the trick-or-treaters with the expression of an entomologist confronted with a particularly outlandish new specimen of beetle. Had he been in America for Halloween before? Napoleon couldn't remember.

"All this dressing up must seem kind of weird to you, huh?"

"Not at all. It's a form of exorcism," said Illya.

Napoleon blinked. "Exorcism?" he said. "Sometimes your mind works in the weirdest ways."

"Look at it from an anthropological point of view. Every culture has its own way of dealing with primal fears, the ancient terrors that lurk below the surface of the conscious mind. Some light bonfires, or burn figures in effigy. Some bring food to graveyards in order to placate the dead. In America, you dress up as your own worst fears. And then you offer up a ritual sacrifice to exorcise them."

"So you're saying being eaten by a zombie is the average American's worst fear?" said Napoleon, with a grin.

"Spare me the relentless literalism. A zombie is clearly a symbol. Like ghosts and werewolves and vampires. They're all things that look human, but aren't. Or rather, things that were human once, but aren't anymore. Humans that have lost their humanity. They would tear the throats out of their own children without blinking. You know there are people like that, Napoleon. Monsters walking around inside a human skin. History is full of examples."

"Not just history," said Napoleon, thinking of the tropical island,with its sun-kissed beaches, and the pretty white house with the laboratory in the basement, where a psychopath tinkered with men's minds. He took a deep breath.

"Illya, what was your greatest fear?"

"I told you," said Illya, moving off. "They didn't get that far. It's in the report. I am fully functional, Napoleon. You needn't worry about me."

"It's in the report," agreed Napoleon, catching up with him. "But you must have thought about it. I mean, even if they didn't. Get that far. It's not the sort of idea you can just forget about. It kept me awake all night, wondering what death they would have found for me."

"You needn't have worried," said Illya. "It was typical Thrush self-promotion. There are far worse ways of dying than anything they could have made you do."

Napoleon thought of Colonel Acevedo, terrified of heights, dragging himself upwards step by vertiginous step to plummet from a skyscraper.

How do you mean, worse?"

"Ambassador van der Loon was in the Resistance during the war. I looked up his record. He was interrogated by the Gestapo for three nights. His brother died under questioning. Do you really think being crushed by a train was the worst death he could imagine?"

"Well, if you put it like that… no," said Napoleon. "At least that was quick. But I guess their options were limited by practicalities. Getting him to torture himself to death would have been kind of tricky."

"So even if they had. Programmed me like that, I mean. It wouldn't have been."

"Wouldn't have been what?"

Illya looked away.

"Is that your worst fear, then?" prompted Napoleon, when the silence showed no signs of ending. "Death by torture?"

Illya shrugged. "Perhaps," he said, at last. It would depend who was doing the torturing. There are worse things than dying."

"There are?" said Napoleon. "Name one."

"Living," said Illya. "When you should be dead." He looked at Napoleon's puzzled face and bit his lip in frustration. "Let me tell you a story," he said. "A Halloween story. But one without candy at the end."

Once upon a time there was a little boy who was taken to see a dead man. The man had been a hero. He had loved his country and everyone had loved him, so they all wanted to come and pay their last respects. The little boy and his mother travelled by train all day and all night to where the man lay in a vast building inside a vast square inside a vast city. The tops of the towers reached all the way the sky, which was full of winter birds, and the streets were full of people, all waiting to see the dead hero. The line stretched down the steps of the building and around the square and through the city for miles and miles.

After many hours of waiting, the part of the line where the little boy and his mother were waiting climbed up an endless flight of steps into a room, lined with white columns and hung with flags as red as blood. An orchestra dressed in black was playing and the air was thick with the scent of lilies. The music and the shuffle of feet were the only sounds. Some of the people were crying, but silently. The tears rolled down their cheeks slowly, like raindrops down a window pane. Others had boarded-up faces, like empty shops.

The man was lying in his coffin with his eyes closed. His arms were folded across his chest. The little boy had never seen a human being who looked so waxy, so glazed, like an expensive doll. His mother had told him that the man's corpse was special, it had been treated so it would never rot away like other, lesser bodies, but would remain immaculate. He had died, she said, but he was not dead. In a way, he would never die.

The smell of lilies and hospitals made the child's head reel. He wanted to run, but the crowd held him close. Suddenly the corpse opened its eyes, as glassy as a teddy bear's, and sat up. The little boy wanted to scream, but he couldn't. The guard of honor reached for him with fingers of white bone, their mouths gaping black and red. Before they could close on him, the press of bodies swept him away from the coffin and out of the hall, but the little boy knew the man who wasn't dead would catch up with him. No matter how fast he ran, he would be eaten in the end.

Napoleon had to clear his throat before he could speak. He wasn't sure what Illya was trying to tell him, but he found himself unexpectedly moved by the bizarre little story. Illya almost never talked about his life before he had come to America, and those fragments he did drop - wolves and grandmothers and homespun pieces of folksy wisdom - sounded more like fairy stories than the iron reality of the Union of Soviet Socialist Republics. This was the first time Illya had even hinted at his political beliefs. You could no more get him to utter a word of criticism of the communist system then you could get him to express overt criticism of UNCLE.

Napoleon knew better than to ask who the little boy had been. Illya would close up like a clam at such a personal question. It couldn't have been Illya himself, he hadn't even been born in 1924. An uncle, perhaps, or an older cousin. Someone who had been close to him. Someone who had whispered stories to him and was now dead, crushed beneath the wheels of the state Illya served.

"Lenin lived, Lenin is alive, Lenin will live," he said.

"That was the slogan," agreed Illya, drily. "You must admit, it verges on necromancy."

Necromancy. A Halloween story. Napoleon thought of what Illya had said about Halloween, about the walking dead, who had lost everything that made them human, yet still wore the faces of the people they had once been. What must it be like, to owe allegiance to a zombie state that devoured its own children; that would, one day, almost certainly devour you? And yet still to feel loyalty to what that state had once been, to the ideals it had once represented? How much candy could you distribute, in a desperate attempt to bring those ideals back to life? UNCLE, he supposed, was once such piece of candy. A ritual sacrifice. An attempted exorcism. Perhaps if you loved hard enough … if you sacrificed enough ... But what if there was nothing left, nothing but the deceitful face of something that had lost its soul?

Napoleon thought of Illya stalking him through the dark garden, his eyes glassy. For a moment he seemed to hear the rustle of the grass as feet moved softly across the lawn, saw the brush of a shadow in the corner of his vision. He thought of Illya moving towards him, his face white and expressionless, his gun raised.

That, he realised with a sudden lucid certainty, had been what Illya was really afraid of. Losing himself. Losing all that made him Illya. Becoming a traitor, a torturer, a monster walking around in human skin. Just like Mother Russia, who tore the throats out of her own children. And they had got that far. Napoleon had been right all along. That insane son-of-a-bitch Partridge had pulled out Illya's darkest nightmare and made it come true, sending him out to kill Napoleon, or to die in the attempt.

"You came back," he said.

Illya looked at him with something so painfully like hope that Napoleon caught his breath.

"How did you know?" said Illya. "You should have shot me, Napoleon. How did you know there was anything of me left?"

Now was not the time for comforting platitudes. Illya deserved an honest answer, however painful. Nothing less than the truth would do.

"I didn't," he said. "I just hoped, that's all."

Illya's lips twisted in a bleak smile.

"Nadezhda umiraet poslednej," he said. "'Hope is the last thing to die'. I wish I had as much faith as you, Napoleon. I would have killed you, you know. Without blinking. After all, I had already done it once."

Napoleon nodded. "I know," he said, quietly. "I suspected all along they'd gone through with it."

"So does Waverly," said Illya. He sighed. "I didn't put it in the report because I was afraid he'd declare me unfit for fieldwork if he knew... what I'd become. Are you going to tell him?"

Napoleon shook his head.

"The real you was still in there. Just like those kids under their white sheets and zombie masks. Maybe the real thing is always still there. Underneath." Underneath the monster. Underneath the purges and the gulags and the interrogation chambers. Because if people like Illya still served the USSR loyally, surely something of all the love and hope that had been poured into her must still remain? Buried deep, certainly, but there. People didn't stop being people just because they behaved monstrously. Even Partridge, psychopath that he was, had been a paid-up member of the human race.

"There's a monster inside all of us," he said, thoughtfully. "It's part of being human. But there's also an us inside every monster, if we could only find a way to bring it out."

A crowd of small ghosts whirled around them, holding hands under their sheets and chanting, "Boo to you." Trapped within the spinning circle, Napoleon dug the mints out of his pocket and dropped one into each eager, grasping hand. The ghosts thrust them into their mouths and scattered away down the street.

Napoleon watched them go. "Maybe I should have offered you candy," he said.

Illya's grin was unexpectedly warm. "It's not too late," he said.

Napoleon grinned back. Nadezhda umiraet poslednej. Illya had got that wrong. The English translation wasn't "hope is the last thing to die." It was far more – well, hopeful.

"Hope springs eternal," said Napoleon.