弗朗索瓦（Philippe Marlaud 饰）深深爱着名为安娜（玛丽·瑞莱 Marie Rivière 饰）的女子，然而，由于工作的缘故，两人几乎无法见面。一次偶然中，弗朗索瓦看到安娜和她的前男友克里斯汀（马修·加里瑞 Mathieu Carrière 饰）在一起，之后，他又发现克里斯汀和另一名陌生女子有所来往。于是，弗朗索瓦起了跟踪克里斯汀的念头。 在跟踪的途中，弗朗索瓦结识了名为露西（Anne-Laure Meury 饰）的女子，在得知了事情的来龙去脉之后，露西对于弗朗索瓦的行为表示了理解，同时加入了他的跟踪队伍中。终于，弗朗索瓦从安娜的口中得知了陌生女子的真实身份，她和克里斯汀是兄妹。同时，露西亦投向了另一个男人的怀抱。The aviator Christian visits his ex-mistress Anne seven o'clock in the morning, to tell her that their affair is over, because his wife is pregnant and will soon move to Paris. Anne's new lover, François, happens to see Christian and Anne when they leave her house, and thinks that their affair is still going on. He tries to contact Anne, but she won't talk to him. At a pavement café François sees Christian and an unknown woman, which he assumes is the aviator's wife. As he is in a bad mood and doesn't know what to do, he decides to follow the couple. On his way through a park he bumps into a cute girl, Lucie, who is 15 years old and has taken a day off from school. Lucie soon brings 20-year-old François to explain to her what has happened to him this morning. She is excited by his story and especially the puzzling parts of it. She joins him in pursuing the couple and thinks out various hypotheses about them. When the couple goes into a lawyer's office, Lucie is sure that the unknown woman is the aviator's wife and that they are seeking a divorce. Later, when François visits Anne he learns that the unknown woman is actually not the aviator's wife but his sister. Anne also confirms that her affair with the aviator is over. When François is going to send Lucie a postcard about this, he happens to see Lucie kissing a boy, which makes him dispirited, as this boy happens to be François' friend and work colleague that he sees every day.