Detective Jonah Pierce has mourned his brother Riley's death for a decade, and he's never managed to heal. He loved Riley too much, and maybe in the wrong way. When a new rash of vampiric murders begins, Jonah's division Arcanum is called in to investigate. Sent to talk to a potential suspect, Jonah gets the shock of his life. But that's nothing compared to what comes later, when betrayal shows itself far closer than he ever expected.

Detectives Jonah and Riley Pierce are back in another case for Arcanum, the US government's paranormal police agency. This time, however, they're headed to Berlin when a series of murders points to the enigmatic leader of a research institute. Things turn personal very quickly, though, and they find themselves in a race to stop a psychopathic mortal hellbent on finding the daywalker gene.