River Marked (Mercy Thompson Book 6);

Being a different breed of shapeshifter-a walker-Mercy Thompson can see ghosts, but the spirit of her long-gone father has never visited her. Until now, on her honeymoon with the Alpha werewolf Adam. An evil is stirring in the depths of the Columbia River-and innocent people are dying. As other walkers make their presence known to Mercy, she must reconnect with her heritage to exorcise the world of the legend known as the river devil...