The Duchess of Acquamonda offers her nephew’s wife jewelry which, they find out are fake. They call famous detective Nick Winter to solve the mystery. As soon as he arrives, Nick finds an anonymous note in his suitcase: “Don’t try to find out the truth or you will create a family drama.” Soon after that, he meets the brother of the young bride, Jean Bressac, an inventor who is short on cash. Nick Winter, disguised, is hired as Jean’s secretary. He discovers that the inventor’s father brings him large sums of money. Winter also finds out the name of the smuggler in Paris but fails to arrest the entire gang. Thanks to the fingerprints, he suspects the old chambermaid who finally spills out the truth: she loaned the jewelry box to her son. After a chase through the country and on a canal, the criminals are arrested.