The Cartographer turned out not to be a person but a room.
Or, more precisely, a person and a room.
An old man named Idris.
Ethan would later learn that Idris hadn't left the chamber in eleven years. He was surrounded on every wall by hand-inked maps that had long since stopped resembling any city Ethan recognized.
Streets bent at angles that hurt to follow.
Some of the ink was black.
A worrying amount of it was the same green-gold as the wards on the stairs.
And if Ethan watched it for too long, he could have sworn it moved.
"A door," Idris repeated after Ethan had explained what he'd heard.
He didn't look up from the section of wall he was retouching.
"A door, you said. Nailed shut."
He paused.
"From which side?"
"I don't know."
Ethan frowned.
"I don't think I was meant to know that much."
"No," Idris agreed.
He finally turned toward Ethan.
"Cthu don't share directions with their prey. The fact that you caught anything at all suggests either extraordinary luck or..."
His ink-stained fingers stopped halfway through another stroke.
"...that the thing inside you isn't hiding it from you anymore."
Ethan's expression tightened.
"Why would it stop?"
"Because it may have stopped treating you as prey."
Idris studied him.
"And started treating you as its last chance."
"Last chance at what?"
"Getting home."
The answer came so simply that Ethan almost wished Idris had made it complicated.
Idris returned to the map.
"Which, Mr. Vane, is either the most useful hostage situation this Vigil has stumbled into in a decade..."
His brush moved carefully across the wall.
"...or a very slow-burning catastrophe wearing a young man's face."
He glanced over his shoulder.
"I'd start preparing for both."
Alistair, leaning in the doorway, exhaled through his nose.
Ethan was beginning to recognize that as his version of a curse.
"How long until we know which?"
"However long it takes the boy to stop flinching and actually listen to it."
Idris's eyes settled on Ethan.
"Which is going to be unpleasant. I won't lie to you about that."
He set the brush down.
"But it is also, currently, the only door out of this room that doesn't end with you on a second pyre."
A faint pause.
"One that works this time."
Ethan looked around the chamber.
At the moving ink on the walls.
At the shape of a city that wasn't quite a city.
At the impossible streets and symbols that seemed to shift whenever he looked away and back again.
Then he thought about the coal beneath his ribs.
Patient.
Furious.
And apparently trapped in exactly the way he was.
He thought, too, about how much easier this conversation would be if he simply allowed himself to be afraid of it.
Instead, some quieter part of him was already working out how to use it.
That unsettled him more than the fear would have.
"Then teach me how to listen," he said.
Idris studied him for a long moment.
Then he picked up his brush again.
"Good."
He turned back to the wall.
"That's the first sensible thing anyone's said today."