Doctor Adrian (Boris Karloff) is a researcher looking for a cure to polio that would benefit his young friend Frances Clifford (Maris Wrixon), who suffers from the disease. His research centers upon the use of spinal fluid in a serum that could return mobility to sufferers of polio. The escape of a circus ape and the injury of its trainer provide an opportunity to test his procedure on Frances and it provides positive but limited results. Hoping to prove his research and cure his friend, Doctor Adrian sets out to use the ape as a means to provide the necessary spinal fluid for completing his research.