Derkhan accepted it. She had no choice. She would not leave him, or Lin. She did not blame him. She wanted him to honour his agreement, to give Yagharek what he wanted.

The stink and sadness of the damp little room overwhelmed her. She muttered something about scouting out the river and she left. Isaac smiled without warmth at her half-hearted excuse.

“Be careful,” he said unnecessarily as she left.

He lay cuddling Lin with his back to the foetid wall.

After a while he felt Lin relax into sleep. He slipped out from behind her and walked over to the window, looked out over the bustle below.

Isaac did not know the name of the street. It was wide, lined with young trees all pliant and hopeful. At the far end, a cart had been parked sideways, deliberately creating a cul-de-sac. A man and a vodyanoi were arguing ferociously beside it, while the two cowed donkeys drawing it hung their heads, trying not to be noticed. A group of children materialized in front of the motionless wheels, kicking a ball of tied rags. They scampered, their clothes flapping like flightless wings.

An argument broke out, four little boys prodding one of the two vodyanoi children in the group. The fat little vodyanoi backed away on all fours, crying. One of the boys threw a stone. The argument was forgotten quickly. The vodyanoi sulked a brief moment, then hopped back into the game, stealing the ball.

Further along the road, a few doors down from Isaac’s building, a young woman was chalking some symbol onto the wall. It was an unfamiliar, angular device, some witch’s talisman. Two old men sat together on a stoop, tossing dice and laughing uproariously at the results. The buildings were bird-limed and grotty, the tarred pavement punctuated with water-filled potholes. Rooks and pigeons threaded through smoke from thousands of chimneys.

Cuttings from conversations reached Isaac’s ears.

“…so he says a stiver for that?…”

“…damaged the engine, but then he was always a cunt…”

“…don’t say nothing about it…”

“…it’s on Dockday next, and she copped a total crystal…”

“…savage, absofuckinglutely savage…”

“…remembrance? For who?”

For Andrej, thought Isaac suddenly, without warning or reason. He listened again.

There was much more. There were languages he did not speak. He recognized Perrickish and Fellid, the intricate cadences of Low Cymek. And others.

He did not want to leave.

Isaac sighed and turned back into the room. Lin squirmed on the floor in sleep.

He looked at her, saw her breasts pushing at her torn shirt. Her skirt rode up her thighs. He looked away.

Since recovering Lin, twice he had woken with the warmth and pressure of her against him, his prick erect and eager. He had rubbed his hand over the swell of her hips and down into her parted legs. Sleep had rolled off him like fog as his arousal grew and he had opened his eyes to see her, moving her beneath him as she woke, forgetting that Derkhan and Yagharek were sleeping nearby. He had breathed at her and spoken lovingly and explicitly of what he wanted to do, and then he had jerked backwards in horror as she began to sign babble at him and he remembered what had happened to her.

She had rubbed against him and stopped, rubbed him again (like some capricious dog, he had thought, appalled), her erratic arousal and confusion absolutely clear. Some lustful part of him had wanted to continue, but the weight of sorrow had shrivelled his penis almost instantly.

Lin had seemed disappointed and hurt, then she hugged him, happily and suddenly. Then she curled up in despair. Isaac had tasted her emissions in the air around them. He had known she was crying herself to sleep.

Isaac glanced out at the day again. He thought of Rudgutter and his cronies; of the macabre Mr. Motley; he imagined the cold analysis of the Construct Council, cheated of the engine it coveted. He imagined the rages, the arguments, the orders given and received that week that cursed him.

Isaac walked over to the crisis engine, took brief stock of it. He sat down, folded paper in his lap, and began to write calculations.

He was not worried that the Construct Council might mimic his engine itself. It could not design one. It could not calculate its parameters. The blueprint had come to him in an intuitive leap so natural that he had not recognized it for hours. The Construct Council could not be inspired. Isaac’s fundamental model, the conceptual basis of the engine, he had never even had to write down. His notes would be quite opaque to any reader.

Isaac positioned himself so that he worked in a shaft of sunlight.

The grey dirigibles patrolled the air, as they did every day. They seemed uneasy.

It was a perfect day. The wind from the sea seemed constantly to renew the sky.

Yagharek and Derkhan, in separate quarters of the city, enjoyed their furtive times in the sun, and tried not to court danger. They walked away from arguments and stuck to the crowded streets.

The sky was riotous with birds and wyrmen. They flocked to buttresses and minarets, crowding the gently sloped roofs of militia towers and struts, coating them in white shit. They stormed in shifting spirals around the Ketch Heath towers and the skeletal edifices in Spatters.

They scudded over The Crow, wove intricately through the complex pattern of air that rose above Perdido Street Station. Rowdy jackdaws squabbled over the layers of clay. They flitted over the lower hulks of slate and tar at the station’s shabby rear, descending towards a peculiar plateau of concrete above a little brow of windowed roofs. Their droppings fouled its recently scrubbed surface, little pellets of white splattering against the dark stains where some noxious fluid had spilled copiously.

The Spike and the Parliament building swarmed with little avian bodies.

The Ribs bleached and split, their flaws worsening slowly in the sun. Birds alit briefly on the enormous shafts of bone, launching themselves free again quickly, seeking refuge elsewhere in Bonetown, skimming over the roof of a smoke-damaged black terrace, in the heart of which Mr. Motley ranted against the incomplete sculpture which mocked him with unending spite.

Gulls and gannets followed rubbish barges and fishing boats up along the Gross Tar and the Tar, swooping down to snatch organic morsels from the detritus. They wheeled away to other pickings, to the offal-piles in Badside, the fish market in Pelorus Fields. They landed briefly on the split, algaed cable that crawled out of the river by Spit Hearth. They explored the rubbish heaps in Stoneshell, and picked at half-dead prey crawling through the Griss Twist wasteland. The ground purred beneath them, as hidden cables hummed inches below the ragged topsoil.

A larger body than the birds rose up from the slums of St. Jabber’s Mound and soared into the air. It sailed at a massive height over the western city. The streets below became a mottled stain of khaki and grey like some exotic mould. It passed easily above the aerostats in the gusting breeze, warmed by the noon sun. It maintained a steady pace eastwards, crossing the city’s nucleus where the five rail lines burst out like petals.

In the air over Sheck, gangs of wyrmen looped the loop in vulgar aerobatics. The drifting figure passed over them serene and unnoticed.

It moved slowly, with langorous strokes that suggested it could increase its speed tenfold suddenly and with ease. It crossed the Canker and began a long descent, passing in and out of the air over the Dexter Line trains, riding their hot exhaust briefly, then gliding earthwards with unseen majesty, descending towards the canopy of roofs, weaving easily through the maze of the thermals gusting up from massive smokestacks and little hovels’ flues.