Eventually, when the temperature fell and they had all forgotten the stink, they had moved. It had been a long, arduous journey through New Crobuzon’s vaulted conduits. Lemuel had led, flintlocks ready. Isaac, Derkhan and Yagharek had to carry the construct, which could not move in the liquid filth. It was heavy and slippery, and it had been dropped and banged and damaged, as had they, falling into the muck and swearing, slamming hands and fingers against the concrete walls. Isaac would not let them leave it.

They had moved carefully. They were intruders in the sewer’s hidden and hermetic ecosystem. They had been keen to avoid the natives. Eventually they had emerged behind Saltpetre Station, blinking and dripping in the waning light.

They had bedded down in a little deserted hut beside the railway in Griss Fell. It was an audacious hideout. Just before the Sud Line crossed the Tar by Cockscomb Bridge, a collapsed building made a huge slope of half-crushed brick and concrete splinters that seemed to shore up the raised railway. At the top, dramatically silhouetted, they saw the wooden shack.

Its purpose was unclear: it had obviously remained untouched for years. The four of them had crawled exhausted up the industrial scree, shoving the construct before them, through the ripped-up wire that was supposed to protect the railway from intruders. In the minutes between trains, they had hauled themselves along the little fringe of scrubby grass that surrounded the tracks, and pushed open the door into the hut’s dusty darkness.

There, finally, they had relaxed.

The wood of the shed was warped, its slats ill-fitting and interspersed with sky. They had watched out of the glassless windows as trains burst by them in both directions. Below them to the north, the Tar twisted in the tight S that contained Petty Coil and Griss Twist. The sky had darkened to a grubby blue-black. They could see illuminated pleasure-boats on the river. The massive industrial pillar of Parliament loomed a little way to the east, looking down on them and on the city. A little downriver from Strack Island, the chymical lights of the old city watergates hissed and sputtered and reflected their greasy yellow glow in the dark water. Two miles to the north-east, just visible behind Parliament, were the Ribs, those antique sallow bones.

From the other side of the cabin they saw the spectacularly darkening sky, made even more astonishing by a day in the reeking dun below New Crobuzon. The sun was gone, but only just. The sky was bisected by the skyrail that threaded through Flyside militia tower. The city was a layered silhouette, an intricate fading chimneyscape, slate roofs bracing each other obliquely below the plaited towers of churches to obscure gods, the huge priapic vents of factories spewing dirty smoke and burning off excess energy, monolithic towerblocks like vast concrete gravestones, the rough down of parkland.