After a world war left the country in ruins, the survivors regrouped, creating four cities. With the population lower than ever, the prison system became impossible to maintain, so the city officials developed the Exile Town system.. Avid-a literal dump for the thieves, Bellicose-caverns for the violent, Clamorite-mountains for the unruly, Delaisse-factories for the addicts and vandals, and Equivox-a lake for the liars. When a young thief learns about the Skeleton Key, a device that can be used to unlock anything, she can't help but to go after it. But there's a catch-in order to unlock the box containing it, she needs a key from each of the exile towns, which turn out to be far more dangerous than she could have imagined.