Following yet another daring robbery, the Minister and the Prefect of Police call on a policeman unknown to Lupin, stationed in Africa: Victor offers to play the part of a clever worldly burglar, Mister Lorchester. In this way, he becomes part of Lupin's gang, whose only task is to arrest him. But to make him look the part, Victor needs a well-funded bank account, which the enthusiastic Préfet immediately opens for him. During his evenings of idleness, Victor Lorchester meets a young woman he believes to be Lupin's friend.