A scientist kidnaps a man and transports him to an island, intent on turning him into a super-being. The man obviously doesn't like this idea, so he tries to escape with the help of the scientist's daughter and a band of half-human, half-animal creatures.

While scuba diving in the South Seas, soldier of fortune Matt Farrell is kidnapped by a swarm of divers under the command of the sinister Steinman, who takes him to the isolated island on which Dr. Gordon lives with his devoted daughter Neva. There, Gordon explains his grandiose plan to use Matt in an experiment to build a superior being who will be able to survive the ravages of pollution and nuclear war that Gordon is certain will soon befall Earth. That night, after Matt is locked in his room, he jimmies the lock and sneaks into the doctor's office. While rifling through the files, he comes upon some newspaper clippings identifying Gordon as a Nobel Laureate professor who was fired from a university along with his scientist wife Mary. Matt then descends into a basement laboratory where he finds a severed head encased in a glass jar. The next morning, Steinman lasciviously leers at Matt and, after warning him about the impossibility of escaping, hints that he knows of his escapade the previous evening. Later, Neva, who worships her father as a genius, becomes upset when Gordon refers to the men and women he has imprisoned in cages for use in his experiments as "subjects." When Gordon sends Neva to examine Matt, Matt asks about her mother. After Neva replies that she was a baby when her mother died, Matt kisses her, and after briefly responding to his embrace, she abruptly leaves. Descending the stairs, Neva opens a secret passage leading into a tunnel. Matt follows and finds her in a cave filled with caged, deformed people, the victims of her father's earlier experiments. When one of the subjects, The Panther Woman, breaks out of her cage and attacks Neva, Matt comes to her rescue. Beginning to fall in love with Matt, Neva questions her father about the ethics of his experiments and asks him to set Matt free. Gordon retorts that he is just trying to save lives and that he plans to implant Matt's brain impulses into a new species of superior beings. Later, Matt surreptitiously watches as a new arrival, Juan Pereira, is rolled on a cart into an operating room. Once Pereira is submerged in a vat of liquid, Neva and Gordon begin surgery, but when some of Pereira's blood accidentally spurts out at Neva, she races panicked from the operating room. Matt follows her as she runs into her bathroom and tries to kill herself by taking a handful of pills. Knocking the pills from her hand, Matt wrestles her to the ground, and as they start to kiss, Steinman and Gordon enter. Gordon then orders Matt taken to the cave to be locked in a cage. Afterward, Neva sneaks into Steinman's room and points a rifle at his head. After forcibly disarming her, Steinman calls her a "dirty whore," prompting Neva to accuse him of wanting Matt for himself. Before Steinman can harm Neva, he passes out from a glass of milk he has just consumed, unaware that Neva had drugged it. Hurrying to the cave, Neva frees Matt, but he insists that she and the group of creatures flee through the tunnel while he takes care of Steinman. After Neva leads the creatures, consisting of The Panther Woman, The Antelope Man, The Bat Man, The Ape Man and The Wolf Woman, through the secret tunnel and into the forest, Matt kidnaps Gordon and enters the forest, hoping to lead Steinman away from Neva. Soon after, Steinman awakens and dispatches three of his thugs to follow Neva while he and the others pursue Matt. Neva, who treats the poor, unfortunate creatures as if they were human, asks The Panther Woman to go back and make sure they are not being followed. When The Panther Woman sees Steinman's three thugs, she pounces on one and kills him. As Gordon and Matt proceed through the underbrush, Matt spies some movement and ties Gordon to a tree while he investigates. When Matt returns, he finds that Gordon is gone. Impatient for The Panther Woman to return, Neva sends The Antelope Man to look for her. The Antelope Man reaches The Panther Woman just as she mauls the other two thugs. As The Panther Woman finishes off one of the men, the other shoots The Antelope Man and manages to fire off a flare to alert Steinman as to their position. Bloodthirsty, The Panther Woman attacks the wounded Antelope Man, but The Wolf Woman, who is in love with The Antelope Man, comes to his rescue, after which The Antelope Man kills The Panther Woman with the butt of the rifle. While Steinman and his men make their way to the point from which the flare was fired, Neva decides they must split up and departs with The Ape Man, who scouts ahead. After several of Steinman's men shoot The Ape Man and take Neva prisoner, Steinman and his thugs attack and kill The Wolf Woman and Antelope Man, but The Bat Man escapes. Alerted by the sound of gunfire, Matt arrives and chases Steinman, who has been wounded. Steinman takes refuge behind some rocks, but by the time Matt walks into his line of fire, Steinman has died. Gordon, who had been freed by Steinman's men, returns to the mansion where, after extracting the files from his office, he runs into the tunnel. The Bat Man has also returned to the mansion and slays the thugs with his fangs. Gordon's progress through the tunnel is blocked by his wife Mary, her face hideously deformed by one her husband's experiments. When Mary threatens him with a knife, Gordon asserts that it was her decision to volunteer for the experiment. Enraged, Mary stabs him and flees. Soon after, Matt and Neva reach the end of the tunnel and find Gordon's body. As Neva cradles her father's dead body, The Bat Man, who had previously been unable to fly, soars off into the horizon.