Rafael by Laurell K. Hamilton

Rafael, king of the wererats, is facing a challenge to his crown. He wants me, one of his closest allies, to help him take down a dangerous opponent unlike any he’s fought before. But some of the wererats fear that Rafael is too dependent on me and my ties to the vampire world. They believe that there is only room in America for one supernatural king, and that Rafael will abandon them as prey for the bloodsuckers.

A new challenger has arisen among Rafael’s enemies… one who is younger, hungrier and has dark secrets that could destroy both the wererats and the vampires. Now, my friend must go into the magical heart of his people to find the power and violence that he needs to save them all – or die trying.