“This section is easier,” whispered Shadrach. “There’s no one on the floor above, it’s just the ceiling of this one. And then above that . . . that’s where our slake-moths hide.”

Before they reached the fourth floor, Isaac tugged at Shadrach and pulled him to a stop. Watched by Shadrach and Yagharek, Isaac whispered again to one of the monkey-constructs. He held Shadrach still as the thing crept with mechanical stealth over the lip of the stairs, and disappeared into the dark room beyond.

Isaac held his breath. After a minute, the construct emerged and waved its arm jerkily, indicated them to come up.

They rose slowly into a long-deserted attic room. A window looked out onto the junction of the streets, a window without glass, whose dusty frame was scuffed with a variety of bizarre markings. It was through this little rectangle that light came in, a wan and changing exudation of the torches below.

Yagharek pointed at the window slowly.

“From there,” he said. “It came from there.”

The floor was littered with ancient rubbish, and thick in dust. The walls were scratched with unsettling random designs.

The room was traversed by a discomfiting river of air. It was a faint current, almost undetectable. In the motionless heat of the dome, it was unsettling and remarkable. Isaac looked around, trying to trace its source.

He saw it. Even sweating in the night-heat, he shivered slightly.

Directly opposite the window, the plaster of the wall lay in shredded layers across the floor. It had fallen from a hole, a hole that looked newly created, an irregular cavity in the bricks that raised to the height of Isaac’s thighs.

It was a glaring, looming wound in the wall. The breeze connected it and the window, as if some unthinkable creature breathed out in the bowels of the house.

“It’s in there,” said Shadrach. “That must be where they’re hiding. That must be the nest.”

Inside the hole was a complex and broken tunnel, carved into the substance of the house. Isaac and Shadrach squinted into its darkness.

“It doesn’t look wide enough for one of those bastards,” said Isaac. “I don’t think they work quite according to . . . uh . . . regular space.”

The tunnel was four feet or so wide, rough-hewn and deep. Its interior was quickly invisible. Isaac kneeled before it and sniffed deeply of the darkness. He looked up at Yagharek.

“You have to stay here,” he said. Before the garuda could protest, Isaac pointed to his head. “Me and Shad here, we’ve got the helmets that the Council gave us. And with this—” he patted his bag “—we might be able to get close to whatever, if anything, is in there.” He reached in and brought out a dynamo. It was the same engine the Council had used to amplify Isaac’s mindwaves, attracting his erstwhile pet. He also brought out a large tangle of metal-sheathed piping, coiled around his hand.