Michel Pepe (LAURENT LUCAS) is a 34-year-old teacher who's traveling with his wife, Claire (MATHILDE SEIGNER), and their three young daughters, Jeanne (VICTORIE DE KOSTER), Sarah (LAURIE CAMINITA) and Iris (LORENA CAMINITA), to see his parents (DOMINIQUE ROZAN & LILIANE ROVERE) in the French countryside.
It's a hot day, however, and the girls are cranky, thus resulting in Michel deciding to stop at a rest stop before turning back to the summer home they're slowly renovating. At the stop, Michel runs into Harry Ballestero (SERGI LOPEZ), a former classmate of his that he can't recall, but who seems to remember a great deal about him.
Although Harry's planning to take his girlfriend, Plum (SOPHIE GUILLEMIN), to Switzerland to see the Matterhorn, he decides to invite themselves back to Michel's place for a drink. Once there, and with it being late, Michel and Claire invite their new "friends" to spend the night, an occurrence that couldn't please Harry any more.
It seems that Harry, who inherited a great deal of money from his father, was always fond of Michel, even going to the point of memorizing the poems he wrote in school and of which Claire was not even aware. Michel and Claire find Harry's behavior a bit odd, especially when he offers to help them financially and then buys them a new truck to replace their broken down car.
Even so, they don't want to be rude and thus find Harry and Plum becoming increasingly ingrained in their daily lives. Yet, Harry's friendly ways and his need to fix any problems that Michel may have soon turns into a troubling fanaticism with dangerous results. As Harry decides to deal with Michel's family, including his brother, Eric (MICHEL FAU), and get the teacher to return to writing, the family discovers that there's a fine line between friendliness and obsession.