English zoology professor George Edward Challenger discovers a "lost world" of Jurassic reptiles isolated within the thick, unexplored Amazon. To prove their existence, he organizes a group expedition with playboy Lord Roxton, American socialites Jennifer Holmes, her brother David Holmes, news writer and photographer Ed Malone and Challenger's colleague and rival Professor Walter Summerlee. Local pilot Gomez and travel guide Costa lead the pack on an awesome havoc-wreaking adventure where dinosaurs from long ago still roam free.