The Unknown Terror

Jim Wheatley disappears while exploring the Cave of the Dead. This disappearance drives his sister Gina Matthews and her husband Dan to lead a new expedition to the shores of the Caribbean. The mystery sets the stage for the perilous journey ahead.

Pete Morgan shows up uninvited, rekindling the old romantic triangle with Gina and Dan. He explains his injuries from a previous expedition and asks Dan to take him along. The tension foreshadows conflicts on the voyage.

Sir Lancelot's cryptic song is believed by Dan to reference the Cave of the Dead. He seeks Raoul Koom to interpret the verses, but Raoul refuses to translate. Despite reluctance, the group prepares to hunt for the cave.

Upon arriving in Raoul's village, locals deny that the cave even exists. Raoul flees, preferring silence over trouble, while Dan, Gina, and Pete press on. The denial deepens the mystery surrounding the expedition.

In Ramsey's home, the group encounters the abusive doctor who treats his servant-wife Concha poorly. Gina notices fungus growing on his canned fruit, suspecting something more sinister. Ramsey insists there is no Cave of the Dead, heightening suspicion.

Concha guides Dan and Pete to a place where they can hear the dead crying beneath the earth. While they are away, Gina is menaced by a foam-covered, plant-like monster that chases her through the jungle, and is killed by two passing men.

Lino, Ramsey's worker, agrees to guide Dan and Pete to the cave entrance for the promised $200. The chance of reward motivates them to venture deeper into the unknown. Tension rises as the group prepares to enter.

Inside the cave, Dan and Pete discover skeletons and the lifeless body of Raoul. A storm floods the cavern, trapping Dan while Pete escapes to safety. The expedition's peril becomes immediate.

When the flood subsides, Pete and Gina return with Lino guiding them deeper into the cave. Lino detonates dynamite to trap them, but the blast triggers a rockslide that kills him. The survivors are left to navigate the wreckage.

Pete and Gina find the cave walls coated with the same fast-growing parasitic fungus seen on Ramsey's fruit. They discover Dan injured, warning about the fungus-covered monsters. Pete fights the creatures with a flaming torch as the fungus slides down the walls.

Pete locates a shaft leading to Ramsey's house and climbs to fetch help. Ramsey initially refuses to assist, claiming the danger is not real. Pete explains that the fungus can now grow in fresh air, forcing Ramsey to admit his role in the outbreak.

Pete yanks Ramsey into the cave to confront him about his creation. Concha triggers explosives to collapse the shaft, and Ramsey is consumed by the advancing fungus. The plan is to seal the cave to prevent the spread and catastrophe.

Dan dies from injuries sustained in the cave collapse. Pete and Gina don diving gear and swim toward the surface, escaping the cavern's deadly grips. The surface arrival marks a hard-won survival.

Pete and Gina finally reach a beautiful tropical beach, out of danger but forever marked by their experiences. They have escaped the Cave of the Dead and Ramsey's fungus, yet the memory of the journey lingers. The ending offers a bittersweet note of survival.