Ship's engineer Andrew Braddock and two other men are floating in a lifeboat in the middle of the Pacific following the wreck of the ship Lady Vain. One dies at sea. After seventeen days at sea, Braddock and the other man land on an island, where the other man accompanying Braddock is promptly killed by animals. Braddock is nursed back to health in the compound governed by the mysterious scientist "Dr. Moreau". Besides Moreau, the inhabitants of the compound include Moreau's associate, Montgomery, a mercenary; Moreau's mute, misshapen servant, M'Ling ; and a ravishing young woman named Maria. Moreau warns Braddock not to leave the compound at night. Moreau welcomes Braddock as an honored guest and willingly shares his fine library, but there are some strange goings-on. One day Braddock witnesses Moreau and Montgomery manhandling a chained creature who is clearly not quite human, and the island is home to more than just this one. The Sayer of the Law recites the laws Moreau passed on to them. Moreau explains that they are, in fact, the hybrid products of his experiments upon various species of wild animal. Braddock is both shocked and curious. Moreau explains that he is injecting the animals with a serum containing human genetic material. At times, the human/animal hybrids still have their animal instincts and don't quite behave like a human which sometimes enrages Moreau, feeling that his experiments haven't worked successfully. That night, as Braddock is reeling from learning the truth, Maria goes to his room where they have sex. It is implied that this is intended by Moreau. The following day, Braddock takes a rifle and leaves the compound, determined to see exactly how the hybrid creatures live. He enters a cave and finds several of them. Just as he is surrounded by them and about to use the rifle to defend himself, Moreau appears and restores order. The Sayer of the Law is the only one of Moreau's experimental beasts who can speak; Moreau calls on him to utter the three laws aloud to the other creatures. This reminds them that they must not attack Braddock. After the Bull-Man kills a tiger, Moreau intends to take it to the "house of pain", his laboratory, as punishment. The Bull-Man panics and runs. Braddock finds it in the jungle, badly injured, where it begs him to kill it rather than return it to the lab. Braddock shoots it, angering the man-beasts, as Braddock has broken the law of killing. Convinced that Moreau is insane, Braddock prepares to leave the island with Maria. Moreau stops them and straps Braddock to the table in his lab. He then injects him with another serum so that he can hear Braddock describe the experience of becoming animalistic. Caged, Braddock struggles to maintain his humanity. When Montgomery objects to this treatment, Moreau shoots him in cold blood. Outside the compound, the angry man-beasts turn on Moreau because by killing Montgomery, he has broken the very rule he expected them to follow. He is killed at the compound's gate while trying to whip his attackers into submission. The man-beasts, now overpowered by their primitive natures, go on a rampage to try and break into the compound and destroy the house of pain as the Sayer of the Law states "There is no law." Braddock, still struggling to remain human, Maria, M'Ling, and the still-coherent and benign beastfolk servant women stave them off and engineer an escape through the compound. Eventually, the man-beasts break in and the compound is burned. In the chaos, the wild animals which Moreau kept for his experiments are turned loose and a battle ensues between them and the hybrids. Most of the man-beasts are killed by the animals or consumed by the fire, the Sayer of the Law's throat torn out by a tiger, the Bear-Man tackled off a roof by a black panther, and the lion-man is mauled by a normal lion. During the final escape, M'Ling risks his life to save his companions from a lion and both fall into a pit trap. Braddock and Maria manage to float away in the lifeboat that Braddock arrived in, but are followed by the Hyena-Man who is one of the last man-beasts. After a battle with each other, Braddock kills the Hyena-Man with a broken oar. Sometime later, they see a passing ship, and the serum has worn off, returning Braddock to his full human state as Maria looks on with catlike eyes.
The movie was filmed in Saint Croix, U.S. Virgin Islands. In terms of casting, Lancaster has been described as perfectly matching Wells' description of Moreau's physical appearance, unlike the other two actors to play the role on screen, Charles Laughton in Island of Lost Souls and Marlon Brando in The Island of Dr. Moreau, both of whom were more portly and with receding hair. Actress Barbara Carrera claims there were three or four different endings imagined, including one in which her character gave birth to a kitten. That version was favored by Producer John Temple-Smith, which actor Michael York flatly refused to do. Director Don Taylor said that he did not take it seriously and the footage was never shot. A comic-book adaptation was released by Marvel Comics the same year. Written by Doug Meonch and illustrated by Larry Hama, the comic-book adaptation had a slightly less happy ending than the film, with Maria reverting into a cat woman just before help arrives.
On review aggregator Rotten Tomatoes, The Island of Dr. Moreau holds an approval rating of 56%, based on 25 reviews, and an average rating of 5.1/10. It's consensus reads, "The Island of Dr. Moreau takes a reasonably entertaining pass at adapting its classic source material, although key scenes are let down by struggles with special effects."
