The Monster That Challenged the World

An underwater earthquake at the Salton Sea opens a crevice, releasing prehistoric giant molluscs into the water. A rescue training parachute jump is attempted nearby, but the patrol boat finds only a floating parachute; one sailor dives in and disappears, while something rises from the water.

With no radio contact from the first patrol boat, Lt. Cmdr. Twillinger orders a second rescue boat to investigate. They locate the deserted vessel, slick with a strange slime, and soon the jumper's body surfaces, blackened and drained.

Twill brings a sample of the slime to the U.S. Navy base laboratory for analysis. He teams up with Dr. Jess Rogers and Gail MacKenzie, recently widowed, to study the specimen and identify the threat.

A young couple vanishes after going for a swim in the area. Navy divers are dispatched to investigate the disappearances and monitor the growing danger in the water.

Navy divers locate a giant mollusc and a large egg along the ocean floor, near where the victims were last seen. The mollusc attacks the divers, killing one of them, while the others attempt to fend off the creature.

The giant egg is collected and brought to the U.S. Navy lab for study and is kept under strict temperature control to prevent it from hatching.

The molluscs escape into the irrigation canal system and begin attacking livestock, a lock keeper, a couple in a tryst, and other people nearby, spreading fear and chaos.

Navy divers locate a cluster of molluscs inside the canal system and deploy explosives to destroy them, attempting to halt their spread and safeguard nearby communities.

Back at the lab, Gail MacKenzie and her young daughter Sandy wait as threats escalate. Sandy secretly turns up the thermostat, worried about the lab rabbits and the cold, altering ambient conditions.

Twill calls the lab and receives no answer, then rushes there to find the hatched mollusc cornering Gail and Sandy in a closet as they flee the monster.

Twill battles the mollusc with laboratory chemicals, a CO2 fire extinguisher, and a live steam line. Reinforcements arrive and shoot the monster, ending the immediate threat to Gail, Sandy, and the others.