Vicarious — Jon F. Merz

When disgraced ex-FBI agent-turned-Boston-cop Steve Curran finds a corpse with no practical explanation for its death, the nightmares start again. Convinced the serial killer that caused his expulsion from the Bureau is once again haunting him, Curran soon learns his theories are all wrong. When the sister of the latest victim, Lauren Fields, uncovers an old journal detailing the hunt for a creature known only as the Soul Eater, she and Curran must confront the very real prospect that the killer is not of this world at all â€" and that his motives have little to do with killing, but all to do with something far, far worse.