A simple civil servant Léon, who has the unusual ability to walk through walls, falls madly in love with a hotel thief by the name of Susan. He poses as Garou-Garou, a dangerous gangster to attempt to woo her affections, but is arrested and sent to jail. While in jail he annoys the guards by walking in and out of his cell, and keeps persuading Susan to cease her criminal way of life. As fundamentally being an honest and law-abiding citizen, he eventually handles back everything he has stolen, is acquitted by the court, and becomes famous and respected. When he learns that Susan is planning to return to England and start a new life, he decides to confess to her his emotions. However, the couple is interrupted by a sudden rush of journalists. Trying to escape in a building, they get cornered on a corridor, and Léon pushes Susan through a nearby wall. But by doing this, he loses his own wall-walking ability, and the film concludes.