Lucie makes her living selling bathing costumes on the beach at Marseilles. Her boyfriend Lucien wants to become a policeman, but is rejected and, instead, is recruited as a secret agent. The couple’s ten-year long relationship looks as if it might be over when Lucie starts to fantasize about another man and Lucien embarks on an impromptu affair with an American woman. Then Lucie discovers a book about the psychology of love and decides to put what she reads into practice...