The four of them walked across the roofworld parallel to the Dexter Line. They were passed in both directions by spitting iron trains, wailing and venting great coughs of sooty smoke into the dwindling light. They trooped slowly onwards, towards the station ahead.

It was not long before the nature of their terrain changed. The sharp-angled slates gave way as the mass of architecture rose around them. They had to use their hands. They made their way through little byways of concrete, surrounded by windowed walls; they ducked under huge portholes and had to scale short ladders that wound between stubby towers. Hidden machinery made the brickwork hum. They were no longer looking ahead to the roof of Perdido Street Station, but up. They had passed some nebulous boundary point where the terraced streets ended and the foothills of the station began.

They tried to avoid climbing, creeping around the edges of promontories of brick like jutting teeth and through accidental passageways. Isaac began to look around, nervous and fitful. The pavement was invisible behind a low rise of rooftops and chimney-pipes to their right.

“Keep quiet and careful,” he whispered. “There might be guards.”

From the north-east, a gouged curve in the station’s sprawling silhouette was a street approaching them, half covered by the building. Isaac pointed at it.

“There,” he whispered. “Perdido Street.”

He traced its line with his hand. A short way ahead it intersected with the Cephalic Way, along the length of which they were walking.

“Where they meet,” he whispered. “That’s our pick-up point. Yag . . . would you go?”

The garuda sped away, making towards the back of a tall building a few yards ahead, where rust-fouled guttering made a slanting ladder to the ground.

Isaac and Derkhan plodded slowly onwards, pushing Andrej gently forward with their guns. When they reached the intersection of the two streets they sat heavily and waited.

Isaac looked up at the sky, where only the high clouds still caught the sun. He looked down, watching Andrej’s misery and imploring gaze creasing his old face. From all around the city the night sounds were beginning.

“There’s no nightmares yet,” murmured Isaac. He looked up at Derkhan, held out his hand as if feeling for rain. “Can’t feel anything. They can’t be abroad yet.”

“Maybe they’re licking their wounds,” she said cheerlessly. “Maybe they won’t come and this—” her eyes flicked up towards Andrej momentarily “—this’ll all be useless.”

“They’ll come,” said Isaac. “I promise you that.” He would not talk of things going wrong. He would not admit the possibility.

They were silent for a while. Isaac and Derkhan realized simultaneously that they were both watching Andrej. He breathed slowly, his eyes flickering this way and that, his fear become a paralysing backdrop. We could take his gag away, thought Isaac, and he wouldn’t scream . . . but then he might speak . . . He left the gag in place.