At the limits of their vision, where the leftward curve shut off the long alley from their view, Jacobs moved fast despite his age and gait. Judah and Cutter followed Ori, the golem loping dark beside them, and Drogon behind, and the others in changing order. The alleyway was full of echoes, of the sounds of all their feet. There were no other sounds, no gunfire of the war, no horns or noise of the Collective or the mayor’s city. Only footsteps on winter-damp brick.

"Where’s he going?" Ori shouted. Cutter turned and saw Rahul, two three seconds behind him, disappear momentarily around the corner and not emerge. Where was he? He had slipped beyond the influence of Jacobs’ reconfiguration, been tipped out into New Crobuzon; he would turn the corner into gods-knew-where.

Jacobs was still running, and was that, was he laughing? They ran faster, and from over the rooftops came light and sound again. Drogon was suddenly slow, and Jacobs was walking, his paint still dripping in his hand, and the alley was ended, and his footsteps were suddenly open as he emerged into a clearing. His pursuers ran out after him. They were in cold wind, in the city again, on the other end of that impossible alleyway.

Rahul was gone, and Drogon. They had stumbled and were lost somewhere in the errant geography. Cutter came forward. Judah walked and the darkness golem walked with him, step for step. Scores of yards away was Spiral Jacobs. He was not even looking at them.

Where were they? Cutter found the moon. He looked down between towers and walls. He was half enclosed. He struggled to make sense of it: this then that monolith spired, and here a minaret, and here one much fatter studded with lights, and above them the huge lines of airships. They were outside the Collective.

Above them an enormous column crowned with radial wires. The Spike. They were in an irregular courtyard. The walls were different stones, in different colours. A shaking came up at them through the concrete. They were high up. Cutter looked down over a spread-out skyline, over the city.

Perdido Street Station. Of course. They were in a huge and empty amphitheatre made by chance, floored with scrub, a little wilderness on the station’s roof. Undesigned, a forgot space in the vastness. The passage that had brought them looked now not like a street but a kink in concrete.

The wall, an edifice of huge bricks that made them feel shrunk to dolls, was broken by the remnants of wooden floors where once this open place had been interior. It was surfaced completely with spirals. A thicket rising, as high as a canopy. Some as intricate and complex as tangled briars, some the simplest snailshell patterns. Thousands. Months of industry. Cutter breathed out. From the very top of the wall descended one black line, through the forest of helix pictograms. A spiral, pinpointing this place.