“I think so.”

“They’re air tubes, leading down to pump stations. Chinamen work the air rooms, mostly—they use coal and big engines to suck the clean air down, so we can breathe it when we’re underneath.”

“Except when the ceiling caves in.”

“Except for that, yeah.”

Rector might’ve asked more questions, but somewhere nearby a moan rose up—forlorn and raspy and wet around the edges.

The boys all froze. Their eyes jerked back and forth, exchanging silent questions and answers. Houjin said, “You wanted to see a rotter, didn’t you, Rector?”

“I never said I wanted to. I just said I hadn’t.”

Another deep, sad groan called out. This one received an answer.

“That’s them,” Zeke whispered. “Down below. Don’t worry too hard. All these buildings are sealed on the ground floor. They can’t get inside.”

“You sound pretty sure of that.”

Houjin said, “He’s right. These buildings get checked all the time, the ones with the bridges and seals. Yaozu doesn’t want leaks any more than the Doornails do—and he’s got more men working for him. He maintains the place.”

Zeke went to the nearest window and hung out of it, turning his neck this way and that to get the best view through his visor. “I don’t see them, but they sound pretty close.”

“Not too close, I hope.” Rector scratched at the back of his hand, but that only made it itch more. He scratched harder, every draw of his dirty fingernails ecstasy and misery.

Zeke looked back over his shoulder and saw him. “Stop doing that. You’ll make it worse.”

“I already figured that out.”

“Then why are you still doing it?”

“I can’t stop.”

Houjin sighed. “We have to get you some gloves.”

“Can you tell where it’s coming from? Listen…” Zeke said, and they all stopped talking.

At first, the only sounds they heard were the filtered hiss of their own breathing and the scraping of Rector’s nails against his skin.

But outside, the mournful, sickly, wordless cries continued.

“Let’s go see if we can find them,” Zeke suggested.

“Do we have to?”

Houjin said, “If we don’t know where they are, we can’t avoid them.”

“I thought we weren’t going down within grabbing distance.”

Zeke hemmed and hawed as he went to the other corner window. “We have to get down and cross one street. There aren’t any bridges into the tower—it’s too far away from the nearest buildings.”

“You two can really try a man’s patience, you know that? You tell me no more stairs, and then there are ladders. You tell me we’re staying out of reach, and then you admit we’re headed into the road where rotters can chase us all they like.”