Ex-police Choucas (Delon), is now a private investigator with his friend Tarpon (Michel Auclair). Mme Pigot asks him to investigate the missing of her blind daughter, Marthe. Inspector Coccioli (Daniel Ceccaldi) tells him to accept the case, pocket the money, and stop there. A young man named Pradier brings a letter from Marthe which explains that she goes away with her boyfriend. At the same time, a pharmacist hires Choucas because he suspects his employee Pérez steals money from the cash register. Choucas follows Pérez to a casino and sees how he wins easily. Mme Pigot and Inspector Madrier are killed [the latter in his attempt to kill Choucas], and Choucas is now wanted by the police.
The movie is fast paced and funny at times. The scene when Choucas is leaving the police headquarters is similar to Le samouraï. Like Costello, Choucas looks at his watch, waves his right hand (left hand in the pocket) to call a taxi - the only vehicle which runs on the street [I think it's even the same location]. Only this time the taxi doesn't stop for Choucas.
There is a scene which reminds me of Plein Soleil: when Choucas and Haymann visits the Spaniard. They climbs the stairs and enter a big room with a beautiful ceiling, where a woman is playing a piano. While in Plein Soleil Elvire Popesco has stopped playing when Delon and Maurice Ronet enter the room, this woman keeps doing it - giving a lovely background music while the two detectives interview the Spaniard.
The ending is hilarious. Choucas the hero enter The Green Hill, a weight loss clinic which is used as a place to produce heroin. The Hydrotherapy room gives a strange feeling like the setting in the James Bond movies and we expect our hero to finish his enemies to the end. However, Choucas is different from such superheroes: soon he is caught, his gun is taken, his nose is broken - also his hand, while another hand is tied to a pipe - and in the attempt to break free his head is spurted with hot steam, and after that his knee is shot. The next scene shows him lying on a hospital bed with a bandage all over his head - only shows one eye and his mouth, one arm and one foot in cast, sipping a bowl of porridge with a straw. Rarely I see such a miserable hero. In the scene where his secretary Charlotte (Anne Parillaud) attends his wound, he cries in pain and she comments that Belmondo would have never made such an unmanly gesture.
Mireille Darc, la grande sauterelle, also makes a brief appearance here. We should not miss her, for she is blatantly addressed by Delon.