After a volcano erupts south of the border, people and animals begin inexplicably dying. Earth scientists Hank (Richard Denning) and Arturo (Carlos Rivas) travel to the small town of San Lorenzo, Mexico to investigate. They soon discover that the eruption cracked open an underground cave that contained hordes of giant prehistoric insects, including the scorpions that have been responsible for the killings. Soon, Hank and Arturo come up with a plan to take these monsters down once and for all.