She finally did, and Chain climbed back down from the roof hatch. He sat near Petrovitch’s head and thumbed through the A to Z, pretending to look at the tiny, dense representation of the Metrozone’s roads.

“How,” he said quietly, “how can it be that the New Machine Jihad thinks it’s Old Man Oshicora? You said he was dead.”

“No, Sonja said he was dead. Hijo said he was dead. I never saw the body: I just went on the information I was given.”

“So is he dead or not?”

“Yeah. Pretty much.”

“Then explain this!” Chain took the rat from Petrovitch and shook it at his good eye. “The Jihad is answering to Oshicora’s name.”

“I had it wrong before. I thought at first it was a name for Oshicora loyalists, the programmers for VirtualJapan.” Petrovitch was resting his head against Madeleine’s thigh as she sat crossways behind him. “It’s not that. It’s the computer itself.”

Chain choked. “Do you know how crazy that sounds?”

Petrovitch squinted up at him. “You’ve read all the wrong books and seen all the wrong films. It doesn’t sound like kon govno to me.”

Chain chewed at the fleshy part of his thumb. “Okay. Let’s accept for a moment that you’re right, and the Jihad is nothing but a rogue computer program with ambition. Why is it identifying with Oshicora?”

“Because, you idiot ment, it’s Oshicora’s computer. He bought a fuck-off quantum machine to run VirtualJapan on. He designed it to replicate a whole country down to the tiniest detail. He intended two hundred million nikkeijen to live in it. Tell me, who do you think he was going to trust to be Shogun of all that?”

“Himself?”

“Yeah. But even he couldn’t be in VirtualJapan, everywhere, all the time. So he had an expert system based on his own personality wired into the deepest workings of the simulation.”

Chain worried at his nail. “You still haven’t explained why, Petrovitch.”

“That’s because why isn’t a question I can answer. How did Oshicora’s simulacrum become the New Machine Jihad? How did it break through its firewall? Does it learn or is it only using pre-existing knowledge? Is it self-aware? Does it think? Is it becoming more rational, or is it homicidally insane?”

“Sam,” said Madeleine, “hush.”

“This is important. We have to know if we can reason with it or not.”

She looked down at him. “We also have to work out what we do if we can’t.”

Petrovitch tried to sit up. He leaned on his injured hand, but still couldn’t feel it. “I don’t know if we can kill something that isn’t alive.”

Chain looked around, through the open doors to where Carlisle and Sonja were standing. “What do we tell her?”

“She’s not a child. Tell her the truth.” Madeleine put her hand between Petrovitch’s shoulders and propped him up.

“We can’t even agree what the truth is,” complained Chain. “What if it is Oshicora?”

“Yobany stos, Chain. Oshicora was competent: the Jihad are oblom! It’s no more Oshicora than I’d be if I put on a funny accent and make my eyes go all slitty. The New Machine Jihad is based on Oshicora, a poor man’s copy and nothing more.”

“It answered to his name.”

“It’s confused.”

Chain looked mildly disgusted. “You don’t feel sorry for it, do you? How many deaths is it responsible for so far?”

“It doesn’t know what it’s doing. It’s two days old and it’s trying to make sense of a whole new world.” Petrovitch wanted him to understand. “It asked for help.”

“My job is to serve the citizens of the Metrozone.” Chain looked at his warrant card, his face on the picture and the gold chip that encoded his biometrics. “The New Machine Jihad isn’t one of them. It’s a threat to the very existence of the city itself. We need to stop it. Find out where the off switch is and use it.”

“So who is this ‘we’ of which you speak?”

Chain turned his card around so that Petrovitch had more than enough time to study it. “Let’s get one thing straight: identity fraud, possession of a firearm, assisting organized crime, info-crime, murder. I usually find it very hard to forget about any of those; it’s only because current circumstances are so far beyond usual that you’re not already doing twenty years in a radiation zone.”

“Let’s get something else straight, Detective Inspector Harry Chain.” Petrovitch used his good hand to draw the Beretta and press the barrel between Chain’s eyes. “I could kill you stone dead and everything you know about me would be spread across the bulkhead behind you. You’d be just one more body on the million-high pile.”

Madeleine reached forward and irresistibly steered Petrovitch’s arm aside.

“Will you two stop it?” she said. “Work out that you need each other. Threats aren’t what you want; it’s cooperation.”

“Never do that again,” said Chain to Petrovitch.

“Throw me in prison after we bring the Jihad under control, fine. Before, and God help me, I’ll pull the trigger.”

Chain found he could move again. “So what are we going to do?”

“Talk to the Jihad.”

“You’ve tried that.”

Petrovitch shook his head. “Not face to face.”

“I can’t even begin to wonder how you’re going to do that.”

“That’s because you lack imagination, Chain.” Petrovitch put his gun away, and looked around at Madeleine. “I have to talk to Sonja.”

“I’ll call her.”

“I have to talk to her alone. Just get me to my feet, and I’ll take it from there.”

Her eyes narrowed and her mouth formed a thin-lipped line. “Remember what I said, Sam.”

“I’m not likely to forget,” he said, and she pulled him up, holding him while blood surged around his neglected extremities.

“You Okay?”

“For the moment.” He walked with exaggerated care to the back of the wagon. “Sonja?”

She stopped listening to the sporadic gunfire which had attracted Carlisle to the street corner, and she turned her head to him. “Are you going to take me to the Jihad now?”

“It’s… complicated,” said Petrovitch. He jumped down, stumbled, ended up resting his bandaged hand on the road. The first sparks of sensation jagged up his arm.

Carlisle was crouched by a wall, looking out into the main road. Madeleine and Chain were in the wagon. Sonja was only a step away, but he was still forced to stand without her help.

“How much do you know about VirtualJapan?” he asked, walking away from the wagon and out of earshot of the others.

“My father would talk about it often, about how it would bring the Japanese diaspora back home. How it was the greatest computer engineering project ever undertaken.”

Despite her evident pride, it wasn’t what he wanted to hear. “I’m talking about the guts of it: how he was going to make it work. Did he ever get technical with you?”

“Once or twice.” She smiled prettily, probably the same smile she used on her father when he tried to explain the interface protocols or the physics engine to her.

“Okay, look. Most of this is guesswork, but as far as I can tell, the Jihad is the moderator part of VirtualJapan, the system that supervises people’s behavior and interaction. Your father based it on his own personality, but since he died, it’s taken on a life of its own. The really complicated bit is that it’s somehow conflated itself with actually being your father. It knows you. It wants to protect you. It will kill everyone who gets in the way. When you’re safely out of the city, it’ll destroy the Metrozone, and create something else: for all I know, that something else is Tokyo.” He dismissed the idea with a wave.

“Stop,” she said, holding up her hand. “The Jihad thinks it’s my father?”

“I don’t think it knows what it is. If it is an AI, then it’s thrashing around in the dark much like the rest of us. But it can’t distinguish between being programmed to protect you and biological imperative: it just assumes that it is your father.” Petrovitch felt tired again, a tiredness that burrowed deep into his bones. “I need to talk to it on its own territory. I need to talk it out of wiping the Metrozone off the map.”