When Isaac finally looked up and around the room, he saw the window by Lublamai’s desk was open, the glass broken and the wooden shutters splintered. He stood and ran over to the knocking window frame, but there was nothing to see inside or out.

Even as Isaac ran from corner to corner under his own raised laboratory, darting between Lublamai’s corner and David’s, whispering idiotic reassurances to the terrified Sincerity, looking for signs of intruders, he realized that a terrible idea had occurred to him some time ago, and had been squatting balefully in the back of his mind. He faltered to a stop. Slowly, he raised his eyes and looked up in cold horror at the underside of the walkway boards.

Fearful calm settled on him like snow. He felt his feet lift, trudging inexorably towards the wooden stairs. He turned his head as he walked, saw Sincerity sniffing gradually closer to Lublamai, her courage slowly returning now that she was not alone.

Everything Isaac saw seemed slowed. He walked as if through freezing water.

Stair by stair he ascended. He felt no surprise and only a very dull foreboding as he saw pools of weird spittle on each stair, saw the fresh scrapings left by some sharp-clawed newcomer. He heard his own heart pulsing with what seemed tranquillity, and he wondered if he was numb to shock.

But when he reached the top and turned to see the hutch thrown on its side, its thick wire mesh burst from within, little fingers of metal exploding away from the central hole, and when he saw the chrysalis split and empty and saw the trail of dark juices dribbling from within its husk, Isaac heard himself cry out aghast and felt his body shudder into immobility as an icy tide of gooseflesh swept him up. Horror billowed up within him and around him like ink in water.

“Oh dear gods . . .” he whispered through dry and quivering lips. “Oh Jabber . . . what have I done?”

The New Crobuzon militia did not like to be seen. They emerged in their dark uniforms at night, to perform duties such as fishing the dead from the river. Their airships and pods meandered and buzzed over the city with opaque ends. Their towers were sealed.

The militia, New Crobuzon’s military defence and its internal correction agents, only appeared in their uniforms, the infamous full-face masks and dark armour, the shields and flintlocks, when they were acting as guards at some sensitive locus, or at times of great emergency. They wore their colours openly during the Pirate Wars and the Sacramundi Riots, when enemies attacked the city’s order from without or within.