A young reporter solves a mystery crime. The fictional reporter is Joseph Rouletabille. He works on a complex, and seemingly impossible, crime in which the criminal appears to disappear from a locked room.
| Actor | Role |
|---|---|
 Serge ReggianiJoseph Rouletabille | Joseph Rouletabille |
 Pierre RenoirProfesseur Stangerson | Professeur Stangerson |
 Janine DarceySylvie | Sylvie |
 Arthur DevèreFather Jacques | Father Jacques |
 Marcel HerrandLarsan / Ballmeyer | Larsan / Ballmeyer |
 Gaston ModotArthur | Arthur |
| LLucien NatRobert Darzac | Robert Darzac |
 Hélène PerdrièreMathilde Stangerson | Mathilde Stangerson |
 Fabien LorisJulien | Julien |
 Robert Le FortSecretary | Secretary |
 Germaine MichelCook | Cook |
 Madeleine BarbuléeChambermaid | Chambermaid |
 Léonce CorneMarquet | Marquet |