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