Young Dr. Larry Forbes (Shepperd Strudwick) has come to France to see his fiancee Madelon (Lynne Roberts) who happens to be Dr. Robert Renault’s (George Zucco) niece. A storm stops Forbes from reaching the Renault estate and his forced to spend the night in an inn.
There he meets Renault’s strange man servant Noel (J. Carrol Naish) and Renault’s gardener who is an ex-con. Noel is an odd looking man and he’s infatuated with Madelon. Forbes ends up switching rooms and the man in what should have been his room is murdered in the night. The next day Noel takes Forbes to the mansion. Later Madelon’s dog is killed and Dr. Renault suspects that Noel did it.
It seems that Noel is Dr. Renault’s experiment and he punishes Noel by locking him up in a cage. Noel escapes and goes with Madelon to the Bastille Day fair where some people make fun of the way Noel dances. Meanwhile the ex-con is planning on kidnapping Madelon and holding her for ransom. Forbes becomes suspicious of Noel and breaks into Dr. Renault’s lab and makes a startling discover.
Dr. Renault’s Secret was made in 1942 and is loosely based on Gaston Leroux’s Balaoo. George Zucco made a living playing mad scientists in the 1940’s. He was also Prof. Moriarty in 1939’s The Adventures of Sherlock Holmes. This film is a cut above the usual mad scientist movies that Zucco starred and it’s pretty entertaining.