Dr. Cameron (George Zucco), a discredited scientist succeeds with his experiment in creating a serum that transforms men into wolf-like creatures. Originally developing this formula to help the world, the scientist decides to use his newly-created subject (Glenn Strange) to exact revenge upon the scientists who were responsible for his ouster from the scientific community. The scientist's daughter Lenora (Anne Nagel) grows wary of her father's actions and shares her suspicions with a newspaper reporter (Johnny Downs). When the scientist loses control of his creature, it falls upon the scientist's daughter and the reporter to stop it.