After a year in the Ugandan jungle, botany professor Charles Decker returns to England with a revolutionary growth serum and a small chimpanzee named Konga. Decker and his assistant, Margaret, begin injecting Konga with the serum, and he grows. When the university dean reproves Decker for discussing his discovery with the press, Decker, now mad with power, hypnotizes Konga and commands him to kill.