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.

Serge Reggiani
as Joseph Rouletabille

Pierre Renoir
as Professeur Stangerson

Janine Darcey
as Sylvie

Arthur Devère
as Father Jacques

Marcel Herrand
as Larsan / Ballmeyer

Gaston Modot
as Arthur

Lucien Nat
as Robert Darzac

Hélène Perdrière
as Mathilde Stangerson

Fabien Loris
as Julien

Robert Le Fort
as Secretary