Back when Harry Bosch was just a rookie homicide detective, he had a mentor who taught him to take the work personally and fight for for every case. That mentor, J.J. Thompson, is dead now, but after his funeral his widow hands Bosch a murder book outlining the unsolved killing of a troubled young man. Bosch brings the murder book to LAPD detective Renée Ballard and asks her to help him find what about the case lit Thompson's fire all those years ago.