Shapeshifting mechanic Mercy Thompson finds her loyalty sorely tested when her former boss and mentor is arrested for murder and left to rot behind bars by his own kind, while she is trying to choose between Sam and Adam, the two werewolves she loves.

Being a mechanic is hard work. Mercy Thompson, for instance, just spent the last couple of months trying to evade the murderous queen of the local vampire seethe, and now the leader of the werewolf pack -- who's maybe-more-than-just-a -friend -- has asked for her help. A book of fae secrets has come to light and they're all about to find out how implacable -- and dangerous -- the fae can be. OK, so maybe her troubles have nothing to do with the job....

Mercy Thompson inhabits two worlds without truly belonging to either. To the human inhabitants of the Tri-Cities she's an oddity, a female mechanic operating her own garage. To the town's darker residents, werewolves, vampires, and fae, she's a walker, a last-of-her-kind magical being with the power to become a coyote. Mercy warily straddles the fine line dividing our everyday world from that darker dimension... 'till a boy, mauled by vicious werewolves...