Unhallowed - Rath & Rune, #1

Monsters. Murder. Librarians. Librarian Sebastian Rath is the only one who believes his friend Kelly O'Neil disappeared due to foul play. But without any clues or outside assistance, there's nothing he can do to prove it. When bookbinder Vesper Rune is hired to fill the vacancy left by O'Neil, he receives an ominous letter warning him to leave. After he saves Sebastian from a pair of threatening men, the two decide to join forces and get to the truth about what happened to O'Neil. But Vesper is hiding secrets of his own, ones he doesn't dare let anyone learn.
Secrets that grow ever more dangerous as his desire for Sebastian deepens.  Because Kelly O'Neil was murdered. And if Sebastian and Ves don't act quickly enough, they'll be the next to die.