CALTIKI, THE IMMORTAL MONSTER

A delirious archaeologist stumbles into his group's camp without his partner, both of whom have been exploring a nearby cave. He quickly goes mad, requiring hospitalization. Their interest piqued by this strange turn of events, the group sets out for the cave.

Once there, they find a deep pool of water, behind which is a large statue of Caltiki, the vengeful Mayan goddess who was ceremonially presented with human sacrifices. Hoping to find artifacts, the group sends one of their own down into the pool. At the bottom, he finds a menagerie of skeletons clad in gold jewelry. Running out of oxygen, he comes back up, clutching as much gold as he can carry. Although wishing that he not go down again, he insists on doing so, suggesting that they could become wealthy from the treasures below. Relenting, they let him descend once more. As he collects more and more treasure, his cable to the surface suddenly begins to move erratically. Fearing for his safety, the group pulls him back to the surface, only to find, upon removing his face mask, that his flesh has been reduced to a decayed mass over his skeleton.

Moments later, the shapeless creature that attacked him rears up from the pool, attempting to digest anyone within reach. One of the group is briefly caught by the arm but is then rescued. As the team escapes, the shapeless mass begins to crawl out of the cave. Nearby, there is a tanker truck full of gasoline. One of the scientists drives the truck directly into the moving mass, which violently explodes and sets fire to the blob, destroying it.

The team returns to Mexico City to take their injured colleague to a hospital. Still on his arm is a small piece of the blob, which is slowly digesting him. The surgeons carefully remove the creature, wrapping it up. They find that his arm is nothing more than a few moist scraps of flesh still connected to the underlying bones. After further experimenting on the creature, scientists discover that it is a unicellular bacterium that quickly grows when in the presence of radiation. A comet emitting radiation, that crosses Earth's path only once in every 850 years, is quickly approaching. At the comet's closest approach to Earth, the remaining piece of the blob removed during the surgery begins expanding to an enormous size and reproducing. Unfortunately, the removed sample of creature is stored in the home of expedition member Dr. John Fielding (John Merivale).

While attempting to convince the Mexican government to send its army to destroy the reproducing blobs, Fielding is arrested, but manages to escape. A colleague finally convinces the authorities to sound an alarm, because the multiplying creatures will soon be beyond even their ability to control. The government marshals a regiment of soldiers equipped with flamethrowers and jeeps and sends them to Dr. Fielding's home. Upon their arrival, they find that the amorphous blobs have continued to multiply and have overrun the house and grounds. Dr. Fielding's wife and child have been forced to hide on a second-floor window ledge to escape being devoured. Fielding arrives just in time to save them, just as the arrayed soldiers lay waste to the creatures with torrents of fire.