Devout Roman Catholic Jean-Louis subscribes to an austere moral code influenced by the philosophy of 17th-century physicist Blaise Pascal. When he spots a pretty girl at church, he promises to one day marry her. But then an old friend introduces him to alluring divorcee Maud. After a conversation about love and credo, the chaste Jean-Louis spends the night at Maud's, conflicted about his desires.

Jean-Louis Trintignant
as Jean-Louis

Françoise Fabian
as Maud

Marie-Christine Barrault
as Françoise

Antoine Vitez
as Vidal

Leonid Kogan
as Concert Violinist

Guy Léger
as Priest

Anne Dubot
as Blonde Friend

Marie Becker
as Marie (uncredited)

Marie-Claude Rauzier
as Student (uncredited)