Inspecteur Marc Ferrot (Yves Montand) is a good cop, a good shooter. One night, when snaring 2 thieves, he meet Sylvia - who is taking photos for her window dressing job. They start an affair. However, Sylvia has another lover and this other man is Ferrot's boss (François Périer), Commissaire Ganay. Knowing that Sylvia deceives him, Ganay kills her. Ganay wants to confess, but his paralyzed wife (Simone Signoret) tells him not to. Meanwhile, all clues point to Ferrot as Sylvia's murderer.
The plots are getting better as the movie goes. Sylvia has 2 lovers, but one is not aware of the other. Ferrot tries not to confront directly the eye-witnesses. When Ganay finally realizes that Ferrot is the other man, he commands his staff to gather all the witnesses and will parade Ferrot in front of them. But that night, Ferrot also realizes that Ganay is his rival and it's a matter of who's killing whom first. To avoid one good witness who remembers him, Ferrot does a very shocking thing: he destroys his good looks. The next day, after the witness describes the killer, Ferrot's staff sees the resembles between the drawing and his boss. He tails Ferrot and witnesses Ganay's widow implores Ferrot to end her life. This police plans to report what he has seen when there is a hold-up at Carrefour. Ferrot may have made a mistake, but he did not kill Sylvia, if Ganay is dead it's self protecting, and as for the widow, it's her last wish. Over all, Ferror is a good cop and the force still need him.