The boisterous, arrogant professor Challenger, a reputed biologist and anthropologist, dares the London Zoological Society to mount an expedition to verify his spectacular claim, without physical proof, that his previous expedition to the Amazonian basin found live dinosaurs. Apart from him and his &#39socialite&#39 counterpart, professor Summerlee, it consists of experienced discoverer Lord Roxbury, the young reporter Ed Malone -who got publicly struck down with Challenger&#39s umbrella at his arrival- and Jennifer Holmes, Malone&#39s news agency&#39s boss&#39s daughter, essentially as conditions for putting up the money. In Brazil they are joined by Jennifer&#39s brother David and local &#39guide&#39 Manuel Gomez. They soon discover the dinosaurs are real and dangerous, like giant spiders, but loose their helicopter and thus are desperate for a way down from the isolated plateau. They learn Roxbury knew about the fate of Burton White, an explorer whose diary they find, thus presume to be dead, in search of diamonds, and confirmation of the local tribe being the lethal guardians of the plateau&#39s secrets, but also get surprising help...