Parisian parents Pierre and Anne go to see a film; it bothers Pierre that Anne rejected his overtures during the movie. Not long afterwards Anne tells Pierre that she 'thinks she fell in love with someone'. Pierre registers the news without reaction. Indeed, both seem determined to remain composed and deal with Pierre's hurt pride and Anne's new interest rationally.
Pierre's discusses the situation with mutual friends Victor and Claire. Their reassurances are little comfort. Anne's new relationship begins to strain at Pierre. There is also the added complication of their 18 month-old son Loulou. Despite the regular presence of a nanny, Laurence, each find reason to claim the other is neglecting him. Paranoia and recrimnation begin to escalate. Fights break out, most bitterly after Pierre discovers that Anne has taken Loulou to her mother's.
Pierre surprises Anne at work and asks to talk. He is more composed and tells her that he has decided he must leave. Anne reciprocates with the news that her affair has ended. Digesting this news with the same outward calm as at the beginning of the film Pierre walks Anne back to their flat. He feels unable to go in. Instead he wanders the streets, lost and unable to hail a stream of passing taxis.