The Boule family leads an existence as happy as it is peaceful. Bill is perfectly integrated into this little family. Boule is doing well at school, his mother gives piano lessons at home, while his father is a well-known illustrator.
Everything goes haywire when the head of the publishing house that publishes Boule's father's cartoons rejects his work. This surly and bitter woman thinks his cartoons are lacking inspiration because his family's happiness is having a very negative effect on his creativity. Boule's father returns home with the firm intention of shaking things up and of waking his family up from their soporific happiness by generating a lot of "silliness."
Boule and Bill, along with Boule's mother, will also join in to make this family "happiness" jump the rails, to the point of making everything explode.