He rubbed the flab below his chin. It itched as his stubble regrew, pushing through his uneven skin. Wind blew through the windows. The house in Pincod was tall and mouldering and full of junkies. Isaac and Derkhan and Yagharek had claimed the top two floors. There was one window on each side, overlooking the street and the wretched little yard. Weeds had burst out through the stained concrete below like subcutaneous growths.

Isaac and the others barricaded the doors whenever they were in: slipped out carefully, disguised, mostly at night. Sometimes they would venture out in the daylight, as Yagharek had now. There was always some reason given, some urgency that meant the vague trip could not wait. It was just claustrophobia. They had freed the city: it was untenable that they should not walk under the sun.

“I know about the commitment,” Derkhan said. She looked over at the loosely connected components of the crisis engine. Isaac had cleaned them up the previous night, slotted them into place.

“Yagharek,” he said. “I owe him. I promised.”

Derkhan looked down and swallowed, then turned her head to him again. She nodded.

“How long?” she said. Isaac glanced up at her, broke her gaze and looked away. He shrugged briefly.

“Some of the wires are burnt out,” he said vaguely, and shifted Lin into a more comfortable position on his chest. “There was a shitload of feedback, melted right through some of the circuits. Um . . . I’m going to have to go out tonight and rummage around for a couple of adapters . . . and a dynamo. I can fix the rest of it myself,” he said, “but I’ll have to get the tools. Trouble is, every time we nick something we put ourselves even more at risk.” He shrugged slowly. There was nothing he could do. They had no money. “Then I have to get a cell-battery or something. But the hardest thing is going to be the maths. Fixing all this up is mostly just . . . mechanics. But even if I can get the engines to work, getting the sums right to . . . you know, formulating this in equations . . . that’s damn hard. That’s what I got the Council to do last time.” He closed his eyes and rested his head against the wall.

“I have to formulate the commands,” he said quietly. “Fly. That’s what I’ve got to tell it. Put Yag in the sky and he’s in crisis, he’s about to fall. Tap that and channel it, keep him in the air, keep him flying, keep him in crisis, so tap the energy and so on. It’s a perfect loop,” he said. “I think it’ll work. It’s just the maths . . .”

“How long?” Derkhan repeated quietly. Isaac frowned.

“A week . . . or two, maybe,” he admitted. “Maybe more.”

Derkhan shook her head. She said nothing.

“I owe him, Dee!” Isaac said, his voice tense. “I’ve promised him this for ages, and he . . .”