The city of Tevanne runs on scrivings, industrialised magical inscriptions that make inanimate objects sentient; they power everything, from walls to wheels to weapons. Scrivings have brought enormous progress and enormous wealth - but only to the four merchant Houses who control them. Everyone else is a servant or slave, or they eke a precarious living in the hellhole called the Commons.
There's not much in the way of work for an escaped slave like Sancia Grado, but she has an unnatural talent that makes her one of the best thieves in the city. When she's offered a lucrative job to steal an ancient artefact from a heavily guarded warehouse, Sancia agrees, dreaming of leaving the Commons - but instead, she finds herself the target of a murderous conspiracy. Someone powerful in Tevanne wants the artefact, and Sancia dead - and whoever it is already wields power beyond imagining.
Sancia will need every ally, and every ounce of wits at her disposal, if she is to survive - because if her enemy gets the artefact and unlocks its secrets, thousands will die, and, even worse, it will allow ancient evils back into the world and turn their city into a devastated battleground.