Robert Sandell, a financially struggling author with an invalid mother, agrees to undergo Dr. Lamb's experimental procedures in exchange for monetary compensation and medical assistance for his mother. Dr. Lamb claims to be researching ways to extend human lifespan. Despite warnings from the doctor's wife and a hunchbacked assistant, Robert consents to being strapped to an operating table. It is only then that he discovers the true purpose of the experiments - Dr. Lamb intends to devolve human subjects into a simian approximation to prove his theory of evolution. However, before Dr. Lamb can proceed, an ape-man, who was set free by the hunchbacked assistant, crushes Dr. Lamb to death.