Alain works together with Lionel at a publishing company, and Lionel is called "sex machine" there for his endless affair. Alain bets Lionel that he couldn't fall with a woman and spend a night with her without having sex. Lionel accepts the bet, and at random choses travel agent Claire.

Lionel is a seducer. His success with women provokes his friend's jealousy. One of them, Alain, challenges him to seduce a beautiful woman chosen at random, to fall in love with her and spend a night with her without making love. Claire is the chosen victim. Behind Claire's prim and proper facade there lurks a lusty, full-blown and demanding sexuality. The self-control that Lionel imposes on himself (with difficulty) to win his bet begins to intrigue Claire. She decides to take the offensive. As Alain tells the story to young Sophie on a café terrace three years later, Lionel's misadventures comically upset several popular prejudices concerning virility and male sexuality.