Inspector Favenin, after being posted away for indiscipline, returns to duty and links up with his old friend Barnero. The two start investigating the murder of Dassa, a bar owner who refused to let his premises be used for distributing the drugs of Tavernier, the local crime lord who is protected by police and politicians. When Dassa's sister arrives to settle his affairs, the goons who murdered her brother beat her up and wreck the bar.

Rover, an old friend of Dassa, hides the girl on his stud farm and decides to get revenge. He enlists Villetti, a fellow ex-mercenary, to murder Tavernier as he leaves his private gambling club. An alibi is secured from a third colleague, Aulnay, who will swear that the two were playing cards with him and his wife. Rover and Villetti succeed in murdering Tavernier but, as they escape along the roof, encounter Favenin and Barnero. The warning shots of the two policemen are returned and Barnero is killed.

When Favenin's demand to lead the hunt for the killer in his own way is accepted, he first tracks down the two goons who were also in the club. After shooting one for failure to co-operate, he gets the name of Villetti from the other. Tracking down Villetti, he explains to him that the only sure way to get revenge will be to shoot him. Villetti agrees, but points out before the trigger is pulled that this makes Favenin no better than a criminal. Meanwhile, the police have tracked down and arrested Rover, who gives nothing away despite being beaten. Favenin tracks down Aulnay, who persists in the false alibi despite a beating.

After this trail of beatings and deaths, Favenin is again suspended and, sending his wife away to safety, stays alone in his riverside home. Aulnay tracks him down and informs both Rover, who is in jail pending trial, and Dassa's sister. The girl goes to confront Favenin, but both are unaware that Rover has escaped. Guessing where he will be heading, a strong force of police surround Favenin's house. When the armed Rover confronts Favenin, police fire brings him down. Favenin hands over a written report of his investigations, which ends with his resignation.

• Michel Bouquet as L'inspecteur Favenin
• Françoise Fabian as Hélène Dassa
• Gianni Garko as Dan Rover (as John Garko)
• Michel Constantin as Viletti
• Rufus as Raymond Aulnay
• Anne Carrère as Christine
• Théo Sarapo as Lupo
• Henri Garcin as Georges Duval, dit 'Georgy Beausourire'
• Pierre Massimi as Robert Dassa
• Bernard Fresson as L'inspecteur Barnero
• Adolfo Celi as Le commissaire principal / Chief of police
• Jean-Claude Bercq as Germain (as Jean-Claude Berck)
• Serge Nubret as Le Noir

• The Cop at IMDb