Dr Bernard Adrian (Boris Karloff) is a kindly, but slightly mad, scientist who seeks to cure a beautiful young woman of polio - the girl reminds the doctor of his late daughter. To find this cure, he needs human spinal fluid to complete the formula for his experimental serum. For this he dresses in an ape skin and chooses his victims based on social standing, his theory being that the health of this pretty girl is more valuable to society than the lives of the poor unfortunate victims. Despite the good intentions of the doctor, he becomes victimised himself by the townspeople as they are suspicious of his actions. By coincidence, a vicious circus ape has broken out of its cage, and is terrorising the town.
