Irwin Allen co-writes and directs this adaptation of Sir Arthur Conan Doyle's fantasy adventure. Professor George Challenger (Claude Rains) assembles an unlikely team of doubting scientists and explorers to investigate an area of the Amazonian jungle where he believes dinosaurs evaded extinction. Upon arrival the group are greeted with the shocking reality of the professor's sensational claims but are prevented from making a quick escape from the prehistoric creatures after their helicopter is destroyed. Stranded in the jungle, the group encounter hostile natives and even more dangerous creatures in the increasingly threatening environment as they try to devise a plan of escape...