Emile is a steelworker in a car factory ;a confirmed bachelor going on fifty, he leads a peaceful life .One night, he is woken up by a burst of machine gun fire. The cafe in the corner of the street has been burglarized.A distraught young girl rushes into his apartment building and hides in his room .When the police make a search, he makes her out to be his lover for the night.Madeleine tells her about her sad past : she has severed all links with her parents ,she's an unwed mother and in the underworld's clutches. Emile sends his protegee to old mommy Dupont's place ,in the suburbs of Paris.

Roger, editor of a women's magazine, meets Roberte, his friend Jean's former mistress, at a major couturier's during a collection presentation. Roberte, who now lives in Florence with her niece Maria, asks Roger to arrange a student exchange so that Maria can come to Paris to perfect her French. Roger approaches Jean's son Philippe, a student at the Beaux-Arts, who agrees to go to Florence. Maria and Philippe meet on the platform at Pisé station. They miss their respective trains and take a walk together. A flirtation begins, then each goes back to the other. Jean finds Maria charming and, like an unrepentant Don Juan, decides to win her over, but thanks to his old maid, his intrigues come to nothing and Maria can marry Philippe.

On this beautiful May 1st, Thérèse is about to give birth. Their presence at home is undesirable, so Jean, her husband, decides to take François, their little boy, to a soccer match. Their plans change when they meet a former factory mate who seems to have made a success of his life. This man, Blanchot, decides to return to Jean a sum of money he had once borrowed. Trusted, Jean is drawn into a clandestine circle, where his apparent luck delivers him without ulterior motive to Blanchot, who is one of the ringleaders. The police interrupt the dangerous game, putting Jean, who has no identity papers, in an awkward situation.

Georges Villard, a minor bank employee, is won over by Mr Steve who does him favours, treats him to the high life and introduces him to his wife Florence, with whom he falls in love. Georges is unaware that these generous gifts will cost him dearly.