The film is also known as Charlie Chan in the Scarlet Clue (American informal title) and Charlie Chan: The Scarlet Clue in Australia. The film is in the public domain due to the omission of a valid copyright notice on original prints.
Charlie Chan and his son Tommy and their block-head driver Birmingham Brown investigate the shenanigans and suspects that results from a furtive gang trying to steal radar secrets from a radio station.
Sidney Toler as Charlie Chan
Benson Fong as Tommy Chan
Mantan Moreland as Birmingham Brown, Chauffeur
Virginia Brissac as Mrs. Marsh
Ben Carter as Ben Carter
Robert Homans as Capt. Flynn
Jack Norton as Willie Rand
Janet Shaw as Gloria Bayne
Helen Deverell as Diane Hall
Victoria Faust as Hulda Swenson / Janet Carter
Leonard Mudie as Horace Karlos
By Monogram Pictures (YouTube) [Public domain], via Wikimedia Commons