The film's prologue involves the death of an Irish commandant during the Irish War of Independence, who is shot by the Black and Tans. The film then skips forward a few decades, to the unveiling of a statue commemorating the war hero. When an Englishman arrives to settle in Ireland, the locals distrust him and soon blame him for the statue's destruction.
An earthquake in the Salton Sea unleashes a horde of prehistoric mollusk monsters. Discovering the creatures, a Naval officer and several scientists attempt to stop the monsters, but they escape into the canal system of the California’s Imperial Valley and terrorize the populace.
Mitch Guthrie is a champion bronco rider in the rodeo who tries to keep his kid brother, Andy, from pursuing the same life.
