Terrence McCaleb is asked by the LAPD to help them investigate a series of murders that has them baffled. They are the kind of ritualized killings that McCaleb specialized in solving with the FBI, and he is reluctantly drawn away from his peaceful new life and back into the horror and excitement of tracking down a homicidal maniac. More horrifying still, the suspect who seems to fit the profile that McCaleb develops is someone he has known and worked with in the past -- Detective Harry Bosch.