Bosch is back in the Open-Unsolved unit after a two-year hiatus. He and his partner David Chu are charged with investigating a cold case that has come back with a very odd DNA hit. A rape-murder from 1989 has returned a positive DNA hit on a suspect...who was born in 1981 and was eight years old at the time of the crime.
Meanwhile, an old enemy from Harry's past has sought him out. Former LAPD Deputy Chief Irvin Irving, once Bosch's nemesis, is now a city councilman and a relentless critic of the LAPD. When Irving's son George is found dead, having apparently jumped from a hotel room at the Chateau Marmont, Irving asks for Bosch specifically to be the investigating officer.
This novel contains examples of:
- Alliterative Name: Irvin Irving.
- Badass Grandpa: Bosch is nearly sixty years old and facing mandatory retirement.
- The Bus Came Back: Bosch's old nemesis Irvin Irving returns six years after being forced out of the LAPD at the end of The Closers. Irving, who defended the LAPD at all costs when he was in it, is now a city councilman who is a relentless opponent of the police department.
- Celebrity Paradox: Bosch's daughter mentions that she's watching Castle. One must wonder if in the Bosch universe there's still a writer named Michael Connelly who Castle has a regular poker game with, and who his most famous creation is.
- The Chessmaster: Kiz Rider, who sent a fake report of a drunk taxi driver to Irvin Irving's office in a complicated gambit to tar him with corruption and cost him his re-election to city council.
- Continuity Nod:
- One of many references throughout the Connelly canon to fictional motion picture company Archway Studios.
- Maggie McPherson, Mickey Haller's ex-wife, is assigned as prosecutor for the Chilton Hardy case.
- Double-Meaning Title: The Drop is the Deferred Retirement Option Plan that fixes a date for Bosch's retirement, a drop of blood on the neck of a murder victim, and how the victim in the A-plot died (he fell off a hotel balcony).
- Dramatic Gun Cock: "Bosch pulled back the slide on the Glock to chamber a round." Harry is deliberately invoking this trope because the Glock wasn't loaded; he did it to scare Chilton Hardy into telling them where the evidence of his crimes is.
- Generation Xerox: Harry is impressed by his daughter Madeline's astute observational skills when he shows her security footage from the Chateau Marmont. And he's further impressed by her skill at target shooting.
- Murder by Inaction: McQuillen the ex-cop eventually admits that, after barging into George Irving's room, he figured out that George was going to kill himself. Rather than do anything to stop Irving's suicide, he went across the street to a diner that had a security camera and waited there until Irving jumped.
- Never Suicide: Averted; the guy everyone thought was a suicide at the beginning actually is a suicide.
- No Name Given: As always in the Harry Bosch universe, the chief of police. In this one the chief grants Irvin Irving's request to have Harry Bosch assigned to investigate his son's death. And in a first, the chief identifies himself as "Marty" when calling Bosch on the phone. (He is finally named as Chief Martin Maycock in the next Bosch novel, The Black Box.
- Real Person Cameo: Real Life LAPD detectives Rick Jackson and Tim Marcia make one of their occasional cameos as minor characters.
- Serial Killer: Chilton Hardy is revealed to have killed 37 people.
- There Are No Coincidences: Bosch says this when grilling Robert Mason, the patrolman who made three separate taxicab DUI arrests at the behest of George Irving.
- Two Lines, No Waiting: Bosch investigates two cases: the apparent suicide of former LAPD Deputy Chief Irvin Irving's son, and a cold case murder that comes back with a very surprising DNA hit. The two cases never intersect with each other.
- Wall Slump: An instance of the non-fatal use of this trope to signify shock. Bosch leaans against a wall and then slides to the floor after going through Chilton Hardy's house of horrors and finding a lot of disturbing things (piles of clothing, photographs, a torture room).
- Wedding Ring Removal: George Irving is found to have taken off his wedding ring before taking a dive off the seventh floor of the Chateau Marmont.
- What the Hell, Hero?: Bosch gives one to old partner Kizmin Rider, who has sold out to LAPD politics.
- What You Are in the Dark: Towards the end of the novel, Bosch figures out that Clayton Pell, an abuse victim of depraved Serial Killer Chilton Hardy, is going to murder Hardy. Bosch races across town and saves Hardy from Pell Just in Time. Afterwards, Harry ponders how he could have kept his realization to himself, and how he might have made a great mistake by preventing Pell's vengeance on Hardy.
- Woman Scorned: Irvin Irving is actually referred to as "a man scorned." Dumped by the LAPD, he went into politics and dedicated himself to screwing the police department over.
- You Just Told Me: How Madeline bluffs her father into admitting that he had a woman over at the house. Bosch is highly impressed by her deduction and interview skills, and tells her so.