In the short story The Fourth Man, Raoul Letardeau is the titular fourth man in a train compartment. The three other men in the train compartment were discussing the case of Felicie Bault. They considered themselves experts in their particular field: the spiritual, the legal and the medical. However they noted that they lacked an important point of view: that of the "man in the street", the personal point of view. By coincidence, Raoul supplied this lack for them.
Raoul was born in a fishing village in Brittany. When both his parents were killed in a railway accident, he was taken into an orphanage run by Miss Slater. There he grew up with Annette Ravel and Felicie Bault and got to know both very well. What happened between the three of them forms the main plot of the story.