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 __APOS__socialite__APOS__ counterpart, professor Summerlee, it consists of experienced discoverer Lord Roxbury, the young reporter Ed Malone -who got publicly struck down with Challenger__APOS__s umbrella at his arrival- and Jennifer Holmes, Malone__APOS__s news agency__APOS__s boss__APOS__s daughter, essentially as conditions for putting up the money. In Brazil they are joined by Jennifer__APOS__s brother David and local __APOS__guide__APOS__ 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__APOS__s secrets, but also get surprising help...