Marcel Franck

A married industrialist maintains three mistresses. On the instructions of his wife, the tax inspector seizes the small notebook where he records his illegal dealings. After a stormy marital explanation, the industrialist decides to reduce his costs by getting rid of his mistresses and expresses the intention of returning to legality. But he realizes that everyone, even his wife, prefers the old situation, fraud and mistresses, thanks to which everyone found his little profit.

Stéphane Petitbourgeois is having trouble with his son-in-law Hubert, who has an extra child every year and is expecting his ninth, making thirteen people in the same apartment. However, a competition promises twenty million to the youngest grandfather of twelve grandchildren. Stéphane begins to encourage Hubert. But Pat became sterile from that day on. Finally, after two years, a child is announced. In fact, triplets were born, and after a few twists and turns, Stéphane became the youngest grandfather of twelve grandchildren.

A man of of principle leads a double life: one for his mistress and one he takes home to his wife.