Eventually he stopped and sat back in his chair, pondering. He grabbed some loose paper and scrawled diagrams on it: mental maps, plans of how to proceed.

Again and again he returned to the same model. A triangle, with a cross firmly planted in the middle. He could not stop himself grinning.

“I like it…” he murmured.

There was a knock at the window. He rose and paced over to it.

A small scarlet idiot face grinned at Isaac from outside. Two stubby horns jutted from its prominent chin, ridges and knobs of bone unconvincingly imitated a hairline. Watery eyes gazed above an ugly, cheerful grin.

Isaac opened the window onto the rapidly dwindling light. There was an argument between klaxons as industrial boats fought to crawl past each other in the waters of the Canker. The creature perched on Isaac’s window-ledge hopped up into the open window-frame, grasping the edges with gnarled hands.

“Wotcher, captain!” it gabbled. Its accent was thick and bizarre. “Saw the red wossname, scarf thing…Says to meself, ‘Time for da bossman!’” It winked and barked stupid laughter. “Wossyer pleasure, captain? Atcher service.”

“Evening, Teafortwo. You got my message.” The creature flapped its red batwings.

Teafortwo was a wyrman. Barrel-chested creatures like squat birds, with thick arms like a human dwarf’s below those ugly, functional wings, the wyrmen ploughed the skies of New Crobuzon. Their hands were their feet, those arms jutting from the bottom of their squat bodies like crows’ legs. They could pace a few clumsy steps here and there balancing on their palms, if they were indoors, but they preferred to careen over the city, yelling and swooping and screaming abuse at passers-by.

The wyrmen were more intelligent than dogs or apes, but decidedly less than humans. They thrived on an intellectual diet of scatology and slapstick and mimicry, picking names for each other gleaned without understanding from popular songs and furniture catalogues and discarded textbooks they could just about read. Teafortwo’s sister, Isaac knew, was called Bottletop; one of his sons Scabies.

The wyrmen lived in hundreds and thousands of nooks, in attics and annexes and behind hoardings. Most picked a living from the margins of the city. The huge dumps and rubbish-heaps at the outskirts of Stoneshell and Abrogate Green, the waste-scape by the river in Griss Twist, all swarmed with wyrmen, squabbling and laughing, drinking from stagnant canals, fucking in the sky and on the earth. Some, like Teafortwo, supplemented this with informal employment. When scarfs flapped on roofs, or chalk marks defaced walls near attic windows, the odds were that someone was calling some wyrman or other for a task.

Isaac foraged in his pocket and held up a shekel.

“Fancy earning this, Teafortwo?”

“Betcha, captain!” shouted Teafortwo. “Look out below!” he added and shat loudly. The stool spattered on the street. Teafortwo guffawed.

Isaac handed him the list he had made, rolled into a scroll.

“Take that to the university library. You know it? Over the river? Good. It’s open late, you should catch ’em open. Give that to the librarian. I’ve signed it, so they shouldn’t give you any trouble. They’ll load you up with some books. Think you can bring them back to me? They’ll be pretty heavy.”