A violent underwater earthquake brings elemental fury to the Salton Sea, a calm, southern California lake, on the shore of which lies an American naval base. From the disturbed depths of the lake, eggs of a prehistoric creature resembling a large worm are opened. A parachutist from the base, the crew of a motor launch and two careless swimmers vanish without explanation in the waters of the lake and shortly after their disappearances, their slime-covered corpses are discovered. Monsters are the cause of the deaths: They feed on human tissue, transforming the bodies into nearly shapeless forms. Because the infamous lake is connected to irrigation sluices that approach the nearby town via underground channels, it is necessary to quickly find the place where the creatures may be hiding. After much searching, they succeed in finding and destroying the nest. Danger seems to have been avoided, but one egg, captured earlier and brought to a laboratory, hatches the last monster, who transforms the lab into a battleground. Lieutenant Commander John Twillinger (Tim Holt), the brave commander of the base, avoids disaster by using a fire extinguisher, a blast of steam and a machine gun to finally destroy the monster.

The story seems more adapted to the nature of Jack Arnold ( It Came From Outer Space), than Arnold Laven, who is sometimes associated with TV and Hollywood westerns. The result, although not exciting, is acceptable. As usual, between shots of the monster, the screenwriters managed to create a love story starring the two main characters: He, the fearless official; she (Audrey Dalton), the young widow who lives for her job and her little daughter. The monster is original enough as a sort of colossal snail, created by Lohman with models of varied size, some of which were animated mechanically.