Book two in the Mercy Thompson series.
Mercy's Vampire customer and possible friend (she not sure vampires can be trusted enough to be true friends) asks her for a favor and she ends up in trouble. A dangerous being is killing people and Mercy must come to the rescue. The vampires either can't or won't help and the being affects the werewolves in a bad way. So it's Mercy (a werecoyote) on a dangerous mission to rescue a vampire and three werewolves.
Mercy just keeps getting more and more interesting. Is it possible that her vampire friend is really a nice vampire? Is is possible he likes her? What about Adam and Sam? What does being a Walker mean? I look forward to the next book.