Maurice Faugel, just released from prison after a six-year sentence, Serge Reggiani re-enters a world of crime and loyalty as he reconnects with an old contact, Gilbert. Gilbert, René Lefèvre, is busy appraising the value of jewels from a recent heist, and Maurice quickly makes it clear that he intends to pull off a robbery the very next day with two accomplices, Silien and Rémy, Jean-Paul Belmondo and Philippe Nahon respectively. The plan is hatched in a haze of old debts and new ambitions, a fragile braid of trust that will soon be tested by violence and shifting allegiances. Maurice kills Gilbert with Gilbert's own gun and steals the jewels along with a substantial sum of cash, a brutal opening move that sets in motion a deadly chain of retribution and misdirection.
It is later revealed that Gilbert had murdered Maurice's girlfriend Arlette to keep her from informing the police when Maurice was imprisoned six years earlier, a revelation that stains Maurice’s sense of motive and loyalty. Maurice leaves the house just as Nuttheccio, Michel Piccoli and Armand, Jacques De Leon—two prominent gangsters—arrive to collect the loot, a tense moment that blurs lines between friendship and criminal obligation. Maurice buries the jewels, the money, and the gun next to a lamppost, a quiet act of concealment that foreshadows the double lives he will try to lead. He then spends the evening at his girlfriend Thérèse's apartment, where Monique Hennessy portrays the complicated tenderness that persists even as danger closes in.
The next day, Silien arrives with Maurice's friend Jean to deliver equipment for the evening’s robbery, a sign that the operation is moving forward despite the lurking threat of police scrutiny. Silien, a man who remains enigmatic even to his closest circle, uses a payphone to contact Inspector Salignari, Daniel Crohem, signaling that he might be maneuvering from the shadows rather than simply serving as a passenger in Maurice’s criminal voyage. The evening of the planned Neuilly burglary arrives, and Maurice and Rémy head out to execute the break-in, while Silien penetrates Maurice’s world from another angle, visiting Thérèse again, then beating her and tying her to a wall radiator while demanding the address of the robbery. The police arrive at the scene of the attempted crime, and Inspector Salignari corners Maurice and Rémy, fatally shooting Rémy. A gunfight erupts between Maurice and Salignari; Maurice is wounded, but Salignari is killed. Maurice leaves the gun beside Rémy’s hand and collapses, his fate hinging on a fragile thread of luck.
Maurice awakens in Jean's apartment, bewildered and uncertain who brought him there. He resolves to find Silien, whom he believes betrayed him by tipping off the police. He entrusts Anita, his girlfriend, with a diagram showing where he buried the jewels, money, and gun, telling her to give it to Jean if something happens to him. The police, convinced that Silien was the informant, pressure Silien to reveal Maurice’s whereabouts, threatening to implicate him in a drug case if he refuses. Silien cooperates enough to get Maurice found, but insists that he did not inform on the botched Neuilly robbery. He does reveal that he believes Thérèse may have been one of Salignari’s informants, a hint that complicates the web of loyalties surrounding Maurice. The car that rescued Maurice is found wrecked, and Thérèse’s body is discovered inside, a grim clue that deepens the sense of a network closing in.
Maurice faces a grim choice: whether to trust Silien or cling to suspicions that he sold him out. The police offer to release him if he provides information about the Neuilly burglary, but Maurice claims he has nothing to offer. He is jailed and meets Kern, a prisoner who will play a pivotal role in the town’s deadly calculus. Silien, meanwhile, obtains the buried jewels, money, and gun by visiting Nuttheccio’s club and speaking with Fabienne, a former girlfriend who becomes entangled in the plot. Fabienne, Fabienne Dali, agrees to testify that Nuttheccio and Armand killed Gilbert if it helps to expose the dangerous alliance surrounding Maurice and Silien. Silien eliminates Nuttheccio and Armand, planting the jewels in Nuttheccio’s safe and convincing Armand that Nuttheccio must be confronted.
Fabienne calls Armand to warn him that Nuttheccio has found the stolen jewels and wants to see him, but Silien’s plan remains to disorient both sides and steer events toward his own quiet exit. When Armand arrives, Silien kills him as well, staging the scene to look like a double suicide, a brutal theater that obscures the true lines of culpability. With Nuttheccio and Armand dead and wrongly framed for Gilbert’s murder, Maurice is released from prison, though the truth of Silien’s role remains murky. Silien’s cunning is underscored by the revelation that he did not inform Salignari about the robbery; instead, he sought to extricate Maurice from prison and secure his own position. Yet Silien’s friendship with Salignari is not simple loyalty: he also recognizes Thérèse as one of Salignari’s informants, a detail that complicates every relationship he touches.
As the night of the robbery winds toward its conclusion, Silien calls Salignari to dinner and learns that the inspector plans to arrest two burglars in Neuilly. Silien uses the opportunity to secure the address from Thérèse and then intercepts Maurice to transport him to Jean’s apartment. The final chapters shift toward Silien’s own next move: he announces that he will move in with Fabienne at his home in Ponthierry, a bid for stability in a life built on unstable foundations. But Maurice, ever calculating, has arranged for his cellmate Kern to kill Silien in prison in exchange for money from the hidden loot. Maurice races to Ponthierry, only to be mistaken for Silien by Kern, who shoots him. Silien arrives to find Maurice dying; Maurice, with his last breath, warns Silien that someone is hiding behind the dressing screen, and Silien shoots at the screen, hitting Kern, who answers with a final, fatal shot. Silien staggers to the phone, tells Fabienne he will not see her that evening, and, adjusting his hat in a mirror, falls down dead, leaving a web of deceit and loyalty that remains unresolved even as the bodies pile up.
