Bosch is on the DROP, which stands for Deferred Retirement Option Plan, which allows him only to work three more years but is seeking an extension to keep doing what he considers his mission in life, catching killers. The reference also seems to reference several aspects of this story; some will be more immediately recognized, like the drop of one victim from a tall building.

Bosch and his partner David Chu are working in the Open-Unsolved unit of the LAPD's homicide squad handling cold cases. They are almost desperate to get back to work when the lieutenant makes her way around the squad room like Santa Claus, parceling out the assignments like presents to the squad’s six detective teams. “Christmas came once a month in the Open-Unsolved Unit. The cold cases were the lifeblood of the unit.”

The first case is the 1989 murder of college student Lily Price who was strangled to death. DNA from a tiny blood smear on her body is matched to recently-paroled child sex abuser Clayton Pell, but Pell was only eight years old when Price died.  Bosch and Chu track Pell to a halfway house for sex offenders, where they meet therapist Hannah Stone.

Pell agrees to meet, and it is learned that during his childhood, his mother dated a man known as "Chill," who sexually abused him and beat him with a belt which could be a way his blood transferred to Price's body since it is likely that a belt was used in the strangulation.

The Price investigation has to slow down to make way for the second case, the death of attorney and business consultant George Irving, who has fallen from a hotel room balcony at Chateau Marmont. George is the son of Irvin Irving, formerly Bosch's nemesis at LAPD, now a city council member and Bosch's frequent foe in power struggles. Irving specifically requests Bosch to investigate his son's death because, despite their antipathy, he believes Bosch is a dedicated detective who will find out the truth no matter what.

As expected, Bosch solves both the cold cases by finding a deranged killer who has been loose in the city for three decades and a political conspiracy that goes back into the dark history of the police department.