“You can’t go into the cave at night.” “It’s always night under the ground.”

Gina Matthews (Mala Powers) and her husband Dan (John Howard) are in Mexico searching for Gina’s brother Jim Wheatley (Charles Gray). His last known location was a village near a legendary cave called “Cave of the Dead”. Pete Morgan (Paul Richards) arrives wanting to join the expedition. Pete was crippled in an accident he blames Dan for. The guys put their past aside to help Gina find her brother.

The group gets a clue to the location of the cave from a calypso song that’s cryptic lyrics could indicate that the cave does exist. Dan believes the cave is near the village of Raoul Koom (Gerald Gilden). Raoul refuses to tell them anything about the cave, or even if the cave actually exists. Undaunted the expedition goes to Raoul’s village. The villagers tell them nothing but they do send them to the home of an American doctor, Ramsey (Gerald Milton).

Ramsey is at home supposedly canning fruit. Ramsey’s wife is a villager named Concha (May Wynn). Ramsey is abusive to her. Pete is attracted to Concha. He convinces her to take him and Dan to where the voices of the dead can be heard from underground. While they are gone a fungus creature attacks Gina. A couple villagers kill the creature and save her.

One of the villagers, Lino (Duane Gray) agrees to take them to the cave for $200. They explore the cave for awhile. Inside they find skeletons from human sacrifices. They also find Raoul’s body. A storm comes up. Dan is trapped inside with rising water and fungus people. When the storm is over Pete and Gina return to the cave to help Dan. Ramsey has been using the fungus from the cave in his experiments. He’s turning villagers into fungus people. Ramsey has Lino set off a dynamite explosion trapping Pete and Gina inside the cave as the fast growing fungus begins to ooze all around them.

“Unknown Terror” was released in 1957 and was directed by Charles Marquis Warren. For the most part, “Unknown Terror” is basically an unknown movie. I consider it to have two monsters. The soap suds fungus and the fungus people. Cool. I’m OK with soap suds monsters.

It’s the plot devises that were strange. Baby brother goes missing so big sis has to find him. Rescue movies usually don’t turn out well for the rescuers, or the rescuees, but fine. First the rescuers need to end up on the shores of The Caribbean and hear a calypso song sung by Sir Lancelot to find out there is a mysterious cave in Mexico called The Cave of Death. Huh? Then they have to happen to find someone from that Mexican village as well.

It’s not believing it all that is the issue. It’s following it all. If you can keep track of everything that gets you to the cave then you can believe in the soap suds monster. How often is the bad guy an actual fungus? Kind of like “Matango: Attack of the Mushroom People” but underground. Short on special effects and dialogue it’s still, for the most part, entertaining. It’s not a great movie and not the worst I’ve ever seen. It’s a basic low budget “B” movie made to pass the time.