Gaston Roudès was the odd-job men of the Belgian cinema :after his version of "La Tour De Nesles" (famous for her orgy scene ,but which was eventually surpassed by Abel Gance's remake ),he tackles the thriller.The title "Une Main A Frappé" (=a hand struck) promised a suspenseful movie;but the plot is so weak even someone who has never read a detective story in his life can guess the whodunit ten minutes after the crime.Besides ,the movie lacks tempo -like his early talkies such as "Le Carillon De La Liberté"- and drags on and on;and if it were not enough,he "explains" his solution as though his audience were all morons.The most pleasant moments are the comic reliefs :Milly Mathis shines in her part of a Marseillaise gossip ,always claiming she can tell the whole thing to a bunch of Concierges;Jeanne Fusier-Gir is a funny two-bit fortune -teller who uses tarots and who claims she is descended from the pharaohs ("just call me Cleopatra",and whose apartment smells of sardines ("it's not sardines ,it's my secret Egyptian herbs").Pierre Larquey (later a teacher in classic "Les Diaboliques") plays two parts :needless to say ,he is more credible as a tramp than as the distinguished owner of a racing stable .