The story a rescue, the rescue of a bad brat's life in the post-WWII period. In 1947, Roger reaches 11 years old. He's a kid badly loved, mischievous and specializes in silly things to do. He is sent to a small boarding school in a small village. Mumu reigns over here. She's not the bitchest school teacher of the area. Roger has already been expelled from several schools and this is his last chance to avoid the reformatory his father has been promising him for a long time. But this is will change with the vigilance of Mumu, who, despite her strict aspects, proves herself to have a big heart.