Unseen — Jordan L. Hawk

Librarian Sebastian Rath and his lover Vesper Rune are tasked with seeking and containing the evil Books of the Bound. But one of the Books has been freed from its prison—and is in the hands of a killer. As more bodies turn up, Sebastian finds himself tempted to use forbidden magic to locate the Book and stop the murderer. And when an unexpected connection to the necromancers who created the Books is revealed, Sebastian must choose just how far he'll go to right the wrongs of the past—even if it means endangering his own future.