Arnold Laven directs this 1950s sci-fi creature-feature centered on prehistoric mollusk hatchlings that emerge from the Salton Sea and terrorize Californians. Navy Lt. Cmdr. Twill (Tim Holt) teams up with scientist Dr. Rogers (Hans Conried) to eradicate the deadly threat. While overgrown slugs with huge, piercing mouths take over the land, Twill falls for lab assistant Gail MacKenzie (Audrey Dalton).