Louis Bourdin, a modest ticket puncher on the Paris metro, is so enamoured of crime fiction that he decides to write his own novel, expecting that one day he will be as famous as Auguste Le Breton. After months of painstaking research, he pens a work of fiction that describes in meticulous detail a train robbery on his stretch of the metro. Unfortunately, Louis has no success getting the book published, as no one seems to believe the robbery is possible. To prove them wrong, Louis decides to enact the robbery himself, with the help of some professional crooks. As luck would have it, Paul Filippi, the aristocrat of crime, has just been released from prison and is preparing his next criminal exploit. To his mind, Louis has conceived the perfect robbery...