[1] Claire (Jean Seberg), a young Englishwoman, lives in Paris with her staid husband, Georges (François Périer), a government archivist, and their two small children.
One day, while attending a fashion show mounted by her friend Madeleine (Micheline Presle), a couturière, Claire meets a lighthearted young Frenchman, Antoine (Jean-Pierre Cassel).
Despite the fact that he is being kept by Madeleine, Claire responds to his advances and returns with him to his luxurious bachelor apartment.
Before long she is visiting him five afternoons a week; evenings and weekends are reserved for Georges and the children.
Madeleine, strong-willed and possessive, learns of the affair and decides to meet the situation directly by inviting Claire and Georges, as well as Antoine, to the same party.