Navy Commander Hal Roberts is assigned to lead an expedition to Little America in Antartica to investigate reports of a mysterious warm water inland lake discovered a decade earlier. His helicopter and its small party, including beautiful reporter Maggie Hathaway, is forced down into a volcanic crater by a fierce storm. They find themselves trapped in a lush tropical environment that has survived from the Mesozoic Era. Fighting carnivorous plants, dinosaurs, and a limited time window, they struggle to survive and repair the helicopter, their only means of escape. They are both helped and hindered by Dr. Carl Hunter, a megalomaniac survivor of an earlier expedition, who has learned to adapt to the hostile environment.