Perdido Street itself was a long, narrow passageway that jutted perpendicularly from BilSantum Street and wound sinuously east towards Gidd. No one knew why it had once been important enough to give the station its name. It was cobbled, and its houses were not squalid, though they were in ill-repair. It might once have described the station’s northern boundary, but it had long been overtaken. The storeys and rooms of the station had spread out and rapidly breached the little street.

They had leapt it effortlessly and spread like mould into the roofscape beyond, transforming the terrace at the north of BilSantum Street. In some places Perdido Street was open to the air: elsewhere it was covered for long stretches, with vaulted bricks festooned with gargoyles or lattices of wood and iron. There in the shade from the station’s underbelly, Perdido Street was gaslit all the time.

Perdido Street was still residential. Families rose every day beneath that dark architecture sky, walked its winding length to work, passing in and out of shadow.

The tramp of heavy boots often sounded from above. The front of the station, and much of its roofscape, was guarded. Private security, foreign soldiers and the militia, some in uniform and some in disguise, patrolled the façade and the mountainous landscape of slate and clay, protecting the banks and stores, the embassies and the government offices that filled the various floors within. They would tread like explorers along carefully plotted routes through the spires and spiral iron staircases, past dormer windows and through hidden rooftop courtyards, journeying across the lower layers of the station roof, looking down over the plaza and the secret places and the enormous city.

But further to the east, towards the rear of the station, spotted with a hundred trade entrances and minor establishments, the security lapsed and became more haphazard. The towering construction was darker here. When the sun set, it cast its great shadow across a huge swathe of The Crow.

Some way out from the main mass of the building, between Perdido Street and Gidd Stations, the Dexter Line passed through a tangle of old offices that long ago had been ruined by a minor fire.

It had not damaged the structure, but it had been enough to bankrupt the company that had traded within. The charred rooms had long been empty of all but vagrants unperturbed by the smell of carbon, still tenacious after nearly a decade.

After more than two hours of torturously slow motion, Isaac and Yagharek had arrived at this burned shell, and collapsed thankfully within. They released Andrej, retied his hands and feet and gagged him before he woke. Then they ate what little food they had, and sat quietly, and waited.

Although the sky was light, their shelter was in the darkness shed by the station. In a little over an hour twilight would come, with night just behind it.

They talked quietly. Andrej woke and began to make his noises again, casting piteous looks around the room, begging for freedom, but Isaac looked at him with eyes too exhausted and miserable for guilt.

At seven o’clock there was a fumbling noise at the heat-blistered door. It was instantly audible above the rattling street sounds of The Crow. Isaac drew his flintlock and motioned Yagharek to silence.

It was Derkhan, exhausted and very dirty, her face smeared with dust and grease. She held her breath as she passed through the door and closed it behind her, releasing a sobbing exhalation as she slumped against it. She moved over and gripped Isaac’s hand, then Yagharek’s. They murmured greetings.

“I think there’s someone watching this place,” Derkhan said urgently. “He’s standing under the tobacconist’s awning opposite, in a green cloak. Can’t see his face.”

Isaac and Yagharek tensed. The garuda slid under the boarded-up window and raised his avian eye quietly to a knothole. He scanned the street across from the ruin.

“There is no one there,” he said flatly. Derkhan came over and stared through the hole.

“Maybe he wasn’t doing anything,” she said eventually. “But I’d feel safer a floor or two up, in case we hear someone come in.”

It was much easier to move, now that Isaac could force the crying Andrej at gunpoint without fear of being seen. They made their way up the stairs, leaving footprints in the charcoal surface.

On the top floor the window frames were empty of glass or wood, and they could look out across the short trek of slates at the staggered monolith of the station. They waited while the sky grew darker. Eventually, in the dim flicker of the orange gasjets, Yagharek clambered from the window and dropped lightly onto the moss-cushioned wall beyond. He stalked the five feet to the unbroken spine of roofs that connected the clutch of buildings to the Dexter Line and to Perdido Street Station. It sat weighty and huge in the west, spotted with irregular clusters of light like an earthbound constellation.

Yagharek was a dim figure in the skyline. He scanned the landscape of chimneys and slanting clay. He was not watched. He turned towards the dark window, indicated the others to follow him.

Andrej was old and stiff, and found it hard to walk along the narrow walkways they forged. He could not jump the five-foot drops that were necessary. Isaac and Derkhan helped him, supporting him or holding him fast with a gentle, macabre assistance, while the other trained their flintlock at his brain.

They had untied his limbs so he could walk and climb, but they had left the gag in place to stifle his wails and sobs.

Andrej stumbled confused and miserable like some soul in the outlands of Hell, shuffling nearer and nearer his ineluctable end with agonizing steps.

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.