LAPD Detective Renee Ballard tracks a terrifying serial rapist whose trail has gone cold, with the help of the newest volunteer to the Open-Unsolved Unit: Patrol Officer Maddie Bosch, Harry's daughter.

Renee Ballard and the LAPD's Open-Unsolved Unit get a hot shot DNA connection between a recently arrested man and a serial rapist and murderer who went quiet twenty years ago. The arrested man is only twenty-three, so the genetic link must be familial. It is his father who was the Pillowcase Rapist, responsible for a five-year reign of terror in the city of angels. But when Ballard and her team move in on their suspect, they encounter a baffling web of secrets and legal hurdles.

Meanwhile, Ballard's badge, gun, and ID are stolen—a theft she can't report without giving her enemies in the department the ammunition they need to end her career as a detective. She works the burglary alone, but her solo mission leads her into greater danger than she anticipates. She has no choice but to go outside the department for help, and that leads her to the door of Harry Bosch.

Finally, Ballard takes on a new volunteer to the cold case unit. Bosch's daughter Maddie wants to supplement her work as a patrol officer on the night beat by investigating cases with Ballard. But Renee soon learns that Maddie has an ulterior motive for getting access to the city's library of lost souls.