An old man named Oscar is "accidentally" run over by a train in France. According to his will, his heirs must wait until the youngest among them (a simpleton named Janot) reaches the age of 21 before the estate can be settled. Janot unfortunately soon after turns up dismembered by a train as well, in another "accident". Then Rosalie and her husband meet untimely deaths, which calls the affair to the attention of a police inspector. A young family member named Collette is next on the killer's list.