The Unknown Terror is a 1957 widescreen American horror science fiction film directed by Charles Marquis Warren and starring John Howard, Mala Powers, Paul Richards and May Wynn. It was produced by Robert Stabler. The narrative follows a group of explorers who, while searching for a missing man, come across the "Cave of the Dead", filled with parasitic fungi and inhabited by foamy, fungus-covered monster men. The film was released theatrically in the US in August 1957 on a double bill with Back from the Dead.
Plot
The mysterious disappearance of Jim Wheatley (Charles Gray) while exploring the legendary "Cave of the Dead" brings his sister Gina Matthews (Mala Powers) and her husband Dan (John Howard) to what Dan calls the "shores of the Caribbean." But at a pre-expedition party, Gina is taken aback when Pete Morgan (Paul Richards) arrives uninvited. Pete, Gina and Dan had been a romantic triangle. Pete saved Dan's life on an earlier expedition, but was injured and now limps on his permanently damaged right leg; after the injury, Gina and Dan married. He convinces Dan to take him on the new expedition.
Sir Lancelot, the King of the Calypso, performs a song with cryptic lyrics that Dan believes refer to the Cave of the Dead: Down, down, down in the bottomless cave/Down, down, down beyond the last grave/If he's got the stuff of fame/If he's worthy of his name/He may get another chance but he's never more the same/He's got to suffer to be born again. But when Dan asks Raoul Koom (Gerald Gilden), whose village is near the cave, to interpret the song, Raoul refuses, saying that it is better for both him and them if he keeps his mouth shut. Nevertheless, Dan, Gina, Pete and Raoul set off in search of the cave.
Upon their arrival in Raoul's village, where the residents deny that the cave exists, Raoul runs away. Dan, Gina and Pete go to the home of "Americano doctor" Ramsey (Gerald Milton). They find him boiling fruit in a large pot and putting it up in mason jars. Ramsey is married to a villager, Concha (May Wynn), whom he treats like a servant. When she drops a jar of fruit, he beats her. Pete stops him, but Gina notices that the fruit has fungus growing on it. Ramsey tells them that he uses the fruit on his research on fungi, bacteria and slime molds. Ramsey also says there is no Cave of the Dead. Dan, Pete and Gina, however, are determined to find it, and Dan offers to pay $200 to anyone in the village who will lead them to the cave.
The situation becomes tense when Concha takes Pete and Dan to a place where they can hear the voices of the dead crying from beneath the earth. While they are gone, a foamy fungus-covered man-monster chases Gina, who has stayed behind, into the jungle. She is saved when two passing men kill the creature.
Lino (Duane Gray), who works for Ramsey, agrees to guide Dan and Pete to the cave entrance for the $200. While exploring the cave, Dan and Pete find several skeletons and Raoul's body. A storm floods the cave, trapping Dan. Pete escapes. After the storm abates, he and Gina return to the cave, again led by Lino. After they enter, Lino sets off a dynamite charge to trap them inside, but it also causes a rockslide which kills him.
Pete and Gina discover that the cave walls are thick with a fast-growing parasitic fungus, the same stuff that grows on Ramsey's canned fruit. They find Dan, his back broken. He warns them of the fungus-covered monster-men in the cave. The man-monsters attack, but Pete fights them off with his flaming torch. The fungus begins sliding in large blobs down the sides of the cave.
Pete finds a shaft that runs to Ramsey's house. Leaving Gina with Dan, he climbs up for help and learns that Ramsey himself has created the monster-making fungus. Ramsey refuses to help until Pete tells him that the fungus, which had so far been unable to live in fresh air, is now growing out of control. "We can't let it out!" exclaims Ramsey. "We can seal it in the cave! Otherwise it'll destroy the world!" Pete yanks Ramsey into the cave with him as Concha sets off explosives to collapse the shaft. The blast kills Ramsey, whose body is then consumed by his fungus.
Dan dies from his injuries. Pete and Gina don the diving gear they've brought along and swim from the cave to the safety of a beautiful tropical beach.