The Sincerest Form of Flattery: The Statford Chronicles

Life was simple for private detective Tom Statford. Sure, being the Keeper, the first, last and only line of defense between gods and mortals could make for interesting times, but a mundane existence in south-eastern Virginia kept things on the boring side of life. Boring, until bodies appear with all the trademarks of ritualistic homicide. Now, the Keeper must not only stop a psychopath, but also the end of the world.

Easy enough, if the killer doesn't find him first.