The Murderer Lives at Number 21 is a 1942 French comedy thriller film by director Henri-Georges Clouzot. Adapted by Belgian writer Stanislas-André Steeman and Clouzot from Steeman's 1939 book of the same title, it was Clouzot's debut feature film as a director. The film is about the hunt by detective Wens for the murderer Monsieur Durand, who leaves calling cards and manages to be everywhere at once. With the aspiring singer Mila Malou, Wens follows clues to a seedy boarding house where he hopes to find the murderer.