DR. RENAULT'S SECRET:Dr. Larry Forbes (John Shepperd). an American scientist, arrives in France to meet his fiancee Madeline Renault (Lynne Roberts) the niece of scientist Dr. Renault (George Zucco).  Forbes is greeted by Noel (J. Carrol Naish) Dr. Renault's peculiar assistant--who also has affections for Madeline.When a series of unexplained murders occur--including one the police believe was intended for Forbes--the American scientist is horror-struck by a most unnerving realization: Noel is a half-man, half-ape created by Dr. Renault!Forbes tries desperately to halt the experiment...but when Noel's animal instincts take over, "there's murder to pay."