It is the final installment of a series Trilogy, which constitutes a melodrama preceded by Un couple épatant, a comedy and Cavale, a thriller.
Police Inspector Pascal Manise walks into a bar where he gets morphine from Freddy, a former dealer of Jacquillat, a drug lord.
Agnès tells Manise that her friend Cécile Coste has invited them to a party he does not want to go but concedes when she agrees to buy him a suit.
In the meantime the police is looking for Bruno Le Roux, a former leftist revolutionary who has escaped from prison, this means that they have to tail Jeanne Rivet, a colleague of Agnès in the same high school where they work as teachers.
That same night, while investigating the murder of a man (who turns out to be Freddy), Manise is approached by Jacquillat, he lets Manise know that the murder can be pinned on Le Roux, they have an unsettled score consisting in a former association where the leaders of the People's Army (including Le Roux) were arrested 15 years ago, the leaders think that it was Jacquillat who betrayed them but he denies it, it was someone else; Manise cannot turn his back on that information because the case is still open, but the reason Jacquillat tells him that is because he wants Le Roux killed during detention by the police, Manise refuses, therefore Jacquillat uses an ace in his sleeve: Pascal shall not receive any morphine for his addicted wife until he kills his man.
Manise gets a call from Cécile: Agnès has fainted at the party, he takes her home and shoots her up himself with the last fix he has, she apologizes and dozes off.
Manise is called, there has been a fire where the firemen have found many guns, in the ensuing investigation they conclude that it was Le Roux, he has left a bunch of evidence behind him and a neighbour gives a full description.
In the meantime Agnès has been increasingly ill due to withdrawal syndrome, Manise has been watching from outside the apartment and even tries to score some dope from a colleague at the police station to no avail.
In the meantime Agnès has gone out looking for a fix, she tries to buy dope from Banane, a petty drug dealer, she is so desperate that she even offers sex in exchange for a score but he refuses.
Agnès wakes up and finds that she cannot remember most of yesterday, she gets ready to leave for school and arranges with Le Roux, who poses as Pierre, to meet at a parking lot later that day.
Pascal, having lost track of Alain, goes to the hospital where Dr. Colinet works, he runs into him at the parking lot, where he inquires about the alternative treatment that he spoke about earlier, but it turns out that the doctor only mentioned a theory.
When asked about Le Roux's whereabouts she refuses to tell him, he unwittingly lets her know about all his known safe-houses and the stake outs that have been set up for him.
As Manise walks out he spots the silver car again and manages to get the driver into his trunk, he drives off to a car stop far away from the city and tells the henchman that Jacquillat leave him and his friends alone, the henchman tells him that accidents happen all the time, Manise is infuriated and hits the man with his gun and leaves.
Olivier, a friend of Pascal's, tells her to avoid going to a public square where there has been a shoot out, most probably linked with Le Roux.
Manise drives to Cécile Coste's place and tells her that Alain is at Claire's, they drive there but she has found nothing, he spots a man spying on them and he runs to him, he presses his gun against his head and tells him that the next time he will shoot, Cécile asks him to let him go, the man is Claire's boyfriend.