Conducting weird scientific experiments, crazed Dr. James Brewster (Bela Lugosi), aided by his colleague Dr. Randall (Henry Hall), has managed to transform himself into a hairy, stooped-over ape-man. Desperately seeking a cure, Brewster believes only an injection of recently-drawn human spinal fluid will prove effective. With Randall refusing to help him, it falls to Brewster and his captive gorilla to find appropriate donors