Beneath Chicago, nine bridges hold the world together. One of them is breaking.
Astrid Eiriksen has spent sixteen years not asking about her mother. She knows the basics: Eir left when Astrid was three. Her father won't explain why. The pendant Eir left behind has started getting warm.
When a busker named Eli leads her beneath Union Station, Astrid discovers the Underhall — a hidden world of dwarven smiths, wight-brokers, and rune-carved tunnels where information is currency and nothing is free. At its heart, a bridge older than the city is fracturing, and its collapse will take Chicago with it.
The bridge wants a keeper. The last keeper was her mother.
With a cult spreading frost through the streets, a detective who won't stop asking questions, and a letter her father kept hidden for sixteen years, Astrid must decide what she's willing to pay to hold the city together — and what she refuses to give.