Annibal Onnis, a good man and major laundry manufacturer, has his wife's necklace stolen by a young starlet, Regina Rex, who has tried to seduce him. He hires two private detectives, Willis Sr. the father, and Willis Jr. the son, to track down the young woman. Tracking her down in La Baule at a beauty contest, Willis Jr. falls in love with Liliane, known as Régina Rex, and sets out to clear her name, convinced as he is of her innocence. After several comic twists and turns (including the temporary loss of the necklace), we learn that the starlet was hired by Mrs. Onnis to have her husband caught in the act of infidelity, a contract between the spouses stipulating that the unfaithful member of the household would pay 100 million francs to the other. Willis's dedication enables Annibal to catch his wife in the act. The Onnis are happily reunited, and Liliane and Willis Jr. look to the future with a smile.