Sir Arthur Conan Doyle's story of an expedition to a remote plateau rumored to be the home of prehistoric beasts, already the basis of a 1925 sci-fi classic, is again brought to the screen in Irwin Allen's lesser version. Claude Rains stars as Professor Challenger, who leads a team of fellow scientists and adventurers deep into the Amazon jungle. The team must battle unforgiving jungle conditions before arriving at the isolated plateau that is their final destination. There they discover a strange group of prehistoric beasts and unexpectedly find themselves in a fight for survival. While the 1925 Harry Hoyt version is still considered noteworthy for its ground-breaking stop-motion effects, Allen relies on enlarged footage of modern-day animals dressed up as their prehistoric counterparts, a technique that has aged less gracefully.~ Judd Blaise, All Movie Guide