“Sam…”

“Yeah, well. This thing was your idea. You could cut me some slack.” He straightened up, pressing a hand into the small of his back. “It’s uncomfortable, awkward and it’s always there. It does some things better, like hitting people really hard, but the stuff I need it to do now? It’s not fantastic. Frankly, I’m bored with it already.”

“Look, I’m sorry,” she started, but he cut her off.

“Yeah, yeah. I know. Come on, we’re almost there, and the clock’s ticking.” He scooped up the handle on his bag and trailed it after him down the slope toward the tunnel’s blind face.

They had left the river behind; the noise of the trickling water, the drips from the ceiling, the occasional soft moan of the wind blowing up through the vast labyrinth had all been silenced. It was just the two of them, and the sounds they made: their breathing, the scratch and creak of material, the unexpected rasp of the Velcro patches on Petrovitch’s courier bag when he opened it again.

“I came up with the plan while I was lying in hospital waiting for them to fix my eyes. I figured I needed to do three things: get Michael out, blindside the UN Security Council, and make it look like I was doing neither. Doing both one and two, maybe half a dozen ways of managing that. All three? That’s where the standing on the remains of the Oshicora Tower every day came in. I’m in full view of the world, in defiance of two UN resolutions, picking up a rock and throwing it away.” He snorted. “They installed cameras on the nearby buildings to watch me better, in case I got carried away and brought in trucks and earth-movers, in case I actually got serious. Didn’t occur to them to install seismometers. Not while they could see me.”

“But if you don’t dig?” Madeleine pressed her fingers into the tunnel wall, a dense aggregate of gray-yellow clay and sand. She could scrape the surface layer away, but it was hard work. “Don’t tell me you use explosives. It’s that Valentina, isn’t it?”

“Leave Tina out of this. She has no idea what I do or where I go, just that I go and do something. If I needed an inexhaustible supply of semtex, I’m pretty certain she could’ve arranged it, just as I’m pretty certain she’d have got found out by you.” Petrovitch sat back against a prop. “Home-made stuff, sure: brew it up by the vat load, until we leave a smoking crater where our bomb factory used to be, and it’s not like we can pop down to the shops for precursor chemicals.”

“So how do you do it? How, on your own, could you have done all this?”

He revealed his hand, and in it was a small black resin sphere, chased with silvery lines.

“An anti-gravity device.”

“No.” He hefted it and held it out for inspection. “This is a singularity bomb. See, it’s a touch smaller, and the pattern on the surface is different—different inside too, of course.”

Madeleine couldn’t see because she was edging back up the tunnel. “Just put it down, Sam.”

“It’s fine.” He tossed it from hand to hand, not remembering for a brief moment that it was going to be difficult for him to catch it again. His arm shot out with a whirr of motors, and the sphere dropped neatly into his outstretched palm. “Excellent. Anyway, it’s not plugged in. Perfectly safe.”

He pushed a thick nail into the blind face of the tunnel, and knocked it in firmly with a lump hammer.

“You do this every single night?”

“Yeah. Don’t need as much sleep as I used to. I program myself for a few hours’ deep sleep, and I seem to manage. Because of that, I am now, according to my calculations, under the Oshicora Tower.” He spooled some double-stranded wire from a hidden reserve inside his bag and stripped the ends with his teeth. He spat out the plastic sleeving. “I only had Old Man Oshicora’s word for this, but he said ‘below this building’ when he talked about the quantum computer he used to run VirtualJapan. The tower went up in twenty-twenty, and there’s no record of a retro-fit. Which means that somewhere in the foundations, there’s a room large enough to fit the computer, an independent power supply and all the cooling it needs.”

She came a little closer. “You could be burrowing down here forever, trying to find it.”

“Except I’m not looking for the room. I’m looking for the shaft that connects it to the tower. It has to be wide enough to get technicians and equipment down to it, and the computer up if there’s a problem.” Petrovitch carried on working, using conducting glue to stick the bare wire to the bomb and holding them in place while they set. “And thanks to the miracle of ground-penetrating radar, I know that that very shaft is a meter and a half straight on.”

Closer still. “You honestly think you can just do this?”

“Yeah. Who’s going to stop me?” He gave the wires an experimental tug, and was satisfied they’d hold. “Unless you’re going to turn me in, I’m pretty confident no one will know I was even here.”

She was opposite him, face to face in the half-light. “But what are you going to do with Michael?”

He raised his eyebrows and blinked repeatedly. “You know, I hadn’t thought that far ahead. Here I am, busting my yajtza to secretly rescue my friend from his concrete tomb, making sure that none of my friends could possibly be indicted as war criminals by the simple expedient of not telling them what I was doing, and I forget to consider the two Security Council resolutions calling for his immediate death should he ever escape. What a mudak.”

“Sarcasm doesn’t become you,” she said, even as she tried to suppress a smile.

“Yes, it does. My voice is permanently stuck between sarcastic and condescending, no matter how hard I try for the dizzying heights of irony. Never mind.” Petrovitch pulled a battery out of his bag and dangled it in front of her eyes. “Let’s do some science.”

“I’ve missed you.”

He had a retort ready. It was on the tip of his tongue and almost out, but he realized in time that the game had changed.

“Yeah. Well. I’m still the guy who hid an AI from his wife and thinks he did the right thing. And until I invent a time machine, I can’t go back and do it differently. Though there is a school of thought that says if time machines were going to be invented, our past would already have been altered, so maybe I did tell you and it was such pizdets I had to create an alternative timeline where I didn’t tell you in order to put it right again.” Petrovitch succeeded in distracting himself. “If this is the best of all possible worlds, it doesn’t say much for the others.”

She enfolded his hands with hers. “I’ve really missed you.”

He shivered. “Talking geek at you always made you horny.”

Madeleine didn’t deny it. “Everybody knew about Michael before I did. I was upset. Really, deeply hurt that you hadn’t told me. The more people asked me, the worse it got. Reporters would needle me with it whenever I made any sort of public statement. It got me so angry, the only way I could deal with it was—”

“To leave me. I know.”

“We’ve really fucked this up, haven’t we?”

“That depends,” said Petrovitch. “We’re fifteen meters below a collapsed building, crouching in a small tunnel cut through unstable quaternary alluvial deposits using miniature black holes, looking for a concrete pipe that might be blocked by fallen masonry, at the bottom of which could be a very crushed computer, while above ground, someone wants us to believe they have a live nuclear weapon ready to re-enact the attack on Paris.” He watched her face fall, then added. “But we’re here together. Where else would I rather be?”

“Martinique?”

“Big volcano. I like my tropical paradises tectonically stable. And mostly above sea level before you suggest an alternative. I remember a conversation I had with Michael—several conversations really, because he’d keep coming back to the same question. He wanted to know about love, and how it worked, and what it looked like, and what it meant. He wanted answers, and I was bad at giving them. That’s not new, though.”