The lie was smooth as glass. Elara had been born in a municipal vent, choking on ash. But the Undercroft was a story told by knockers to each other—a network of pre-Arc subway tunnels where the air was still cold and clean. No one had ever found it. But believing it existed was the only thing that kept them walking the bridges at dawn.

“Don’t,” Elara said, her voice flat from years of not using it.

She found the girl on the parapet of the Meridian Bridge—a place where the rich went to feel the wind and the poor went to disappear. The girl was maybe twelve, barefoot, her nightgown stitched with the emblem of a high-family. But her face was smeared with the same grey ash as Elara’s own.

Above them, the Arc hummed its failing song. And somewhere in the city, a thousand other knockers were tapping their canes against the walls, telling each other the same lie, leading the same lost children down the same impossible tunnels.