 Scot Webster tries to save his sister Susan from the clutches of gangster W.S. Bruhl. When Scot comes to Bruhl s rented room, one of the gangster s aides falls into his hands, killed by a gunman. The murderer tosses his gun to Scot and disappears. Since all the evidence points at him, Scot is arrested, tried and sentenced to death. A mad scientist uses his brain to transplant it into a gorilla. After the operation Scot wakes up in the body of a gorilla, eager to get his revenge...