19th-century Paris. At a certain aristocrat's home, the theft of a necklace occurs. Because of this a maid and her son Raoul are turned out of the house; ten years later, he has become a prodigy at Sorbonne University and is popular around the city. The nanny who has been looking after him, Victoire, is an author; her novel The Gentleman Thief becomes a best-seller and the protagonist Arsène Lupin is loved as an idol by the people. But the book is prohibited from sale, and in order to save his aunt and to have his revenge on those responsible for the earlier incident, Raoul hits upon the idea of becoming Arsène Lupin. He once again meets Agnes, whom he served in the aristocrat's home, and together they realize their love for each other.