In the port of Amsterdam, a trunk containing a drugged man and top-secret scientific documents from the Ministry of National Defense is discovered. In order to find the source of the leaks and dismantle the spy organization, the authorities call in an unusual personality: Arsène Lupin. The gentleman burglar begins an investigation across the city. He befriends a young woman, Hélène, who belongs to the organization, and manages to get in touch with its leader.