Based on H. G. Wells' novel The Island of Dr. Moreau, this horrifying film about a scientist changing animals into humans was banned in England and parts of the United States.
Edward Parker (Richard Arlen) is rescued from the sea and recovers from his trauma on board the Covena. He sends a telegram to his fiancée Ruth. Captain Davies (Stanley Fields) says the animals in cages are going to Dr. Morreau's island. Edward knocks out the drunk captain and notices fur on a man. The captain throws Parker onto Moreau's boat. Dr. Moreau (Charles Laughton) takes Parker to his house, using his whip to scare away the man-like creatures in the jungle. Moreau tells Lota (Kathleen Burke) not to speak of him or the house of pain and takes her to Parker. Evolved from a panther, she is the only woman on the island, and Moreau wants to see if she can bear a child. Parker hears the house of pain and sees Moreau doing vivisection. He escapes but is surrounded by the creatures. Moreau asks them, "What is the law?" They reply it is not to walk on all fours and not to spill blood, repeating, "Are we not men?" Moreau gives Parker a gun and asks him to come back to the house. Moreau explains how he bred orchids and left England after he moved on to experimenting with animals. Moreau made the creatures from animals, developing speech. He makes sure his boat is wrecked so that Parker cannot leave.
Ruth (Leila Hyams) asks Captain Davies about Parker and gets Captain Donohue (Paul Hurst) to take her to the island. Lota asks Parker to talk to her and jealously throws his book into the water. He says he is in love with someone else but kisses her. Parker complains about her to Moreau, hits him, and threatens to make him stop. Lota cries, and Moreau says she is human; thus he is not Satan. Donohue and Ruth find their way to Moreau and Parker. Moreau offers hospitality and safe travel in the morning; but a creature climbs into Ruth's room. Moreau's assistant Montgomery decides to leave too and helps Parker. Moreau get Ouran to strangle Donohue. The creatures say he broke the law not to spill blood. They realize Moreau can die, and they tell him the law is no more. They say he made them part man and part beast. Lota jumps on a creature following Parker, Ruth, and Montgomery. Parker hears her dying words, "Go back." The three escape as the creatures take tools from the house of pain, and flames engulf the compound.
This nightmarish movie explores fears that scientists will create animals that seem human but still are beasts. Since humans evolved from lower animals, other animals might evolve into human-like creatures. The heroes escape the experimentation, and the creatures revolt from their master, who used pain as his primary method of behavior modification.