The parents of Thérèse and Denise Voise have just passed away and Thérèse delays entering a convent to take care of her younger sister. Max, a young mechanic and unrepentant seducer, takes advantage of Denise, who then tries to commit suicide. To make amends, Thérèse requests that Max marry Denise. He pretends to accept, while in fact planning to in turn seduce Thérèse. She is not immune to his charms, but can nevertheless see what he's up to. Faithful to her religious commitment, Thérèse determines to save this lost soul.