In the 1970s, Fred Wilson, an executive of the Petrox Oil Company, forms an expedition based on infrared imagery which reveals a previously undiscovered Indian Ocean island hidden by a permanent cloud bank. Wilson believes the island has a huge deposit of oil. Jack Prescott, a primate paleontologist, sneaks onto the expedition's vessel and attempts to warn the team against traveling to the island, citing an ominous final message about "the roar of the greatest beast" from previous doomed explorers. Wilson orders Prescott locked up, claiming that he is really a spy from a rival corporation. The ship happens upon a life raft which carries the beautiful and unconscious Dwan. Upon waking, Dwan tells Prescott that she is an aspiring actress who was aboard a director's yacht which suddenly exploded. During the rest of the ship's voyage, Prescott and Dwan become attracted to each other.