Returning from jail Tony le Stéphanois (Jean Servais) finds his girl with another gangster, Grutter (Pierre Grasset). He decides to take another robbery job he has been offered, but makes it more ambitious. With his friends, Jo and Mario, they recruit an Italian safebreaker (Cesar (played by Dassin himself).

Jo has a wife, Louise (Janine Darcey) and 5yo son who he dotes on. Cesar is a womaniser and falls for a singer in Grutter's club, Viviane (Magali Noel).

The planning and execution of the heist go well - with some tension and difficulty - but as they are leaving Cesar holds back to steal a ring that he was looking at when casing the joint. This is their downfall as he gives it ti Viviane, who assumes it is fake, but when Grutter sees it he realises it must mean Cesar is a member of the gang and plots to steal the jewels from them.

Grutters gang kidnap Cesar and force him to reveal Mario's involvement. They kill Mario and his girlfriend and then and try to track down where Jo and Tony are hiding, but not before they sell the jewels and 120 million francs in a suitcase are received. Unable to find where they are hiding  Grutter resorts to kidnapping Jo's young son. Tony uses his contacts to track down where they are holding him and effects a recue but not before Jo has caved in to the kidnappers demands. He arrives with the suitcase and is shot, Tony then arrives back at the kidnappers hideout having discovered that Jo has gone and a shootout ensues. Wounded he goes back to where he left the boy and drives him back to Jo's appartment where Lousie is waiting, crashing the car and dying as he gets there. Lousie rushes down to get her son and the police arrive and get the suitcase.