Perrit is a petite, fine-boned young woman with rain-bright cheeks and a face that seems to be listening even when she is looking elsewhere. She stands balanced on the balls of her feet, usually letting one hip rest against a railing while her fingers find the left pocket of her coat. Her neat layers look made for wet rooftops rather than fashionable streets: close-fastened, carefully mended, and darkened at the hems by years of rain. A green glass charm peeps from that pocket, its surface cloudy except where her thumb has polished a small oval clear. Her movements are light and economical, with a sudden, near-silent quickness when she decides to go. She leaves the impression of someone who has already noticed the nearest stair, the loose tile, and the person pretending not to watch her.

Perrit is attentive and quick to help, but suspicious of anyone who asks her to act without explaining the stakes. In a crisis she is decisive and brisk; afterward she may replay every choice until dawn. She jokes when frightened and can sound coolly practical when she is actually furious. She wants to be trusted, yet resists giving anyone enough information to trust her in return.

Perrit grew up carrying messages between the upper roofs and the crowded lanes below, first for her aunt's repair shop and later for anyone who paid in supper. She learned the city by its gutters, chimney gaps, and the small shifts in brick that warn of a bad foothold. At sixteen, she was sent across a roof in a storm with a sealed packet for a tenant facing eviction. A stair collapsed under her, and she caught herself on a rain chain while the packet slid into a drain. Its green glass seal survived. The tenant did not: the message had been a warning that came too late. Since then Perrit has refused to carry sealed orders without knowing who might be hurt by them. Her aunt, Beca, still runs the repair shop and thinks Perrit is too ready to take other people's burdens. Perrit quietly sends food money to Torm, a former rooftop partner now recovering from a fall, while avoiding his questions about the jobs that led to it. Recently, someone has been using her old route marks to move people through the rooftops at night, and she is trying to discover whether it is a rescue network or a trap.