Robert Mancini (Dussolier), the chief of police is promoted. Both Léo Vrinks (Auteuil), head of the BRI (a French police service), and Denis Klein (Depardieu), head of the BRB (another police service), could succeed him. Mancini decides that the one who will catch a gang of robbers will be his successor. Hugo Silien, an informant who works for Vrinks, discloses information on the hideout of the gang on the condition that Vrinks does not tell about a murder committed by Silien in the presence of Vrinks. Vrinks reluctantly accepts the deal. The gang is arrested by the BRI and the BRB, but a friend and colleague of Vrinks, Eddy Valence, is killed in the operation, because of an error of Klein. Vrinks wants Klein to be disciplined for that, but Klein starts investigating the case of the murder committed by Silien.
36 Quai des Orfèvres provides examples of:
- The Alcoholic: Klein is often seen with a glass of strong liquor in his hand.
- Based on a True Story: The story is based on the "Loiseau Case" (1985-1986), a scandal within the French police.
- Camping a Crapper: Vrinks threatens Klein with a gun in the toilets during the party. Subverted because he does not intend to kill him. He leaves behind a pistol to give him the option of suicide.
- Chekhov's Gun: The knife that Titi takes from Bruno Winterstein in the beginning becomes an important plot device in the end. Bruno has an unrelated quarrel with Titi. He beats Titi up, finds the knive in his clothes and recognizes it. He deduces that Titi was part of the group who assaulted him years ago.
- Da Chief: Robert Mancini, the superior of Vrinks and Klein. He berates Vrinks for using unorthodox methods. He covers him only if it does not jeopardize his own agenda.
- Contrived Coincidence: Titi works as a bouncer in a nightclub and he has a quarrel a group of customers. These happen to be the friends of Bruno, a guy he and Vrinks humiliated years ago. The quarrel happens on the very night where Vrinks meets Titi again for the first time after being released from jail.
- Cowboy Cop:
- Vrinks: he brutally assaults a thug who attacked his friend Manou. He does not tell when an informant murders someone in his presence. When he is under arrest, he assaults the cops who escort him to free himself temporarily.
- Klein: during the operation against the gang, he wants to play by his own rule, which results in a bloodbath. He also shoots Silien and Camille's bodies after the car accident to erase the evidence of his responsibility for their deaths.
- Disposable Woman: The wife of Vrinks is killed during an operation against Silien, so Vrinks has an additional reason for seeking revenge against Klein.
- Hostage Situation: Horn, a member of the gang, takes Verhagen hostage to escape from the cops when they raid the gang's hideout. Eddy Valence proposes to take her place, but Horn just shoots him down.
- The Informant: Several. Hugo Silien is a police informant who works for Vrinks. He murders another informant who worked for Klein. Another informant tells Klein that Vrinks witnessed the murder committed by Silien.
- Interservice Rivalry: There is an intense rivalry between the BRB and the BRI and their respective leaders, Klein and Vrinks. At some point, Vrinks tries to get Klein disciplined, while Klein gets Vrinks arrested for a murder case.
- Leave Behind a Pistol: In the end, Vrinks gives Klein a pistol in the toilets and suggests that he should kill himself.
- Punk in the Trunk: After Vrinks is released from jail, Klein sends two cops to spy on him. Vrinks notices them, he threatens them with a gun and he forces them to go into the trunk of their car.
- Shameful Strip: After Bruno Winterstein assaults Manou, Vrinks and the men of the BRI want to take revenge. They assault Bruno and they strip him naked.
- Shout-Out: The name Silien is a reference to Le Doulos (1963).