Robert (Andre Dussolier) is a stylish and neurotic 50-year-old with an insatiable appetite for women. One day, he reluctantly accompanies his sister to the hospital where her friend Claire (Emmanuelle Devos) has just given birth. Claire is an old flame of Robert's, and the combined impact of seeing her again and the fact that she has used his name for one of her babies makes Robert realize he is still in love with her. As Claire already has a new partner, the father of her child, Robert is particularly shocked and horrified by this discovery. At a bistro later that same day, he gets a second shock in the form of Marie-Pierre (Helene Fillieres, the sister of the film's director, Sophie Fillieres), a young waitress he's chatting up. In the course of their flirtation, Marie-Pierre makes Robert an offer: she will fall in love with him and conduct a full-blown love affair. This makes Robert feel pretty good, so he accepts, but soon enough he discovers that Marie-Pierre, who is nicknamed Aie (French for "ouch") is a bit of a twisted sister. Prone to vomiting up everything she eats and brushing her teeth compulsively with airline toothbrushes given to her by her pilot father, Marie-Pierre gives Robert's brain pause for thought even as his hormones are stampeding blindly ahead. But before he can break off his involvement with her, Robert decides to pay a visit to Claire's apartment, where he finds Marie-Pierre, and the two end up hiding in a closet together and resuming their affair. On a subsequent visit to her parents' house, Marie-Pierre shares some even more bizarre details about her already off-kilter personal history.