LAPD Detective Harry Bosch crosses paths with FBI profiler Terry McCaleb in the most dangerous investigation of their lives. Meanwhile, Terry McCaleb is enjoying an idyllic retirement on Catalina Island when a visit from an old colleague brings his former world rushing back. It's a murder, the unreadable kind of murder he specialized in solving back in his FBI days. The investigation has stalled, and the sheriff's office is asking McCaleb to take a quick look at the murder book to see if he turns up something they've missed. McCaleb's first reading of the crime scene leads him to look for a methodical killer with a taste for rituals and revenge. As his quick look accelerates into a full-sprint investigation, the two crimes - his murdered loner and Bosch's movie director - begin to overlap strangely. With one unsettling revelation after another, they merge, becoming one impossible, terrifying case, involving almost inconceivable calculation. McCaleb believes he has unmasked the most frightening killer ever to cross his sights. But his investigation tangles with Bosch's lines, and the two men find themselves at odds in the most dangerous investigation of their lives.