River Marked (Mercy Thompson, Book 6);

Car mechanic Mercy Thompson has always known there was something different about her, and not just the way she can make a VW engine sit up and beg. Mercy is a shapeshifter, a talent she inherited from her long-gone father. She's never known any others of her kind. Until now.

An evil is stirring in the depths of the Columbia River-one that her father's people may know something about. And to have any hope of surviving, Mercy and her mate, the Alpha werewolf Adam, will need their help...