On the eve of his wedding, on holiday on the Lake Annecy shore, a career diplomat visits an old acquaintance, perhaps a former girlfriend. Through her he meets an intense teenager, Laura, and then lusts after her sister, Claire. Whilst Laura attempts to flirt with him, his fantasy becomes focused on wanting to caress Claire's knee.

Frederic leads a bourgeois life; he is a partner in a small Paris office and is happily married to Helene, a teacher expecting her second child. In the afternoons, Frederic daydreams about other women, but has no intention of taking any action. One day, Chloe, who had been a mistress of an old friend, begins dropping by his office. They meet as friends, irregularly in the afternoons, till eventually Chloe decides to seduce Frederic, causing him a moral dilemma.

"Professor Marian died under mysterious circumstances."