They carried the girl Wren, her name turned out to be, spat at them by a mother who had been in the crowd the whole time, too frightened to speak up until the danger had passed down into the Vault.
This time, nobody argued about it.
"Explain it to me again," Alistair said once she was settled, once Marguerite had posted herself by the door like Wren might bolt, or worse.
"You shut a door. What door?"
"The one I've been learning to open." Ethan sat heavily, the coal in his chest still simmering with something that felt uncomfortably close to resentment. "Idris taught me to listen to mine. I didn't think about what would happen if I did the opposite while another one's screaming at it to come out."
"You closed ranks against your own passenger," Idris said slowly, "to keep it from answering a call from a different Cthu."
"Is that bad?"
"It's unprecedented, which in my experience is usually worse than bad."
Idris crossed to where Wren lay and checked her pulse with two fingers, the same way Alistair had checked Ethan's a week and what felt like a lifetime ago.
"Cthu do not, as a rule, call to one another. They compete for hosts. They do not coordinate."
"Mine called hers kin," Ethan said.
The room went very still.
"Kin," Alistair repeated.
"Not prey. Not rival. Kin."
"I think"
Ethan stopped.
He reached inward, found the coal sulking and furious and, underneath that, something he was beginning to recognize as fear.
He pulled the thread of that fear toward the surface, gently, the way Idris had taught him.
"I think they came from the same place. Karrathess. I think there's more than one door, or maybe one door with more than one thing trying to get through it, and mine's been trying to reopen it since the moment it landed in me."
"And tonight," Marguerite said quietly from the doorway, "it very nearly got a second key."
Nobody answered immediately.
Idris straightened.
For the first time since Ethan had met him, the old man looked less like a scholar and more like a man doing arithmetic he didn't like the answer to.
"How many Taken has this city burned in the last year?" he asked the room, though it wasn't really a question.
His eyes moved from Ethan to Wren.
"How many doors were we closing, and how many were we, without knowing it, leaving ajar?"
Nobody answered.
Nobody needed to.