During World War I, a German U-boat sinks a British passenger ship and takes the survivors aboard. After getting lost in fog, the submarine surfaces near the unknown island of Caprona, a lost world where they find dinosaurs and Neanderthals.

Major Ben McBride organizes a mission to the Antarctic wastes to search for his friend who has been missing in the region for several years. McBride's party find themselves in a world populated by primitive warriors and terrifying prehistoric creatures, all of whom they must evade in order to get back safely