Theboisterous,arrogantprofessorChallenger,areputedbiologistandanthropologist,darestheLondonZoologicalSocietytomountanexpeditiontoverifyhisspectacularclaim,withoutphysicalproof,thathispreviousexpeditiontotheAmazonianbasinfoundlivedinosaurs.Apartfromhimandhis'socialite'counterpart,professorSummerlee,itconsistsofexperienceddiscovererLordRoxbury,theyoungreporterEdMalone-whogotpubliclystruckdownwithChallenger'sumbrellaathisarrival-andJenniferHolmes,Malone'snewsagency'sboss'sdaughter,essentiallyasconditionsforputtingupthemoney.InBraziltheyarejoinedbyJennifer'sbrotherDavidandlocal'guide'ManuelGomez.Theysoondiscoverthedinosaursarerealanddangerous,likegiantspiders,butloosetheirhelicopterandthusaredesperateforawaydownfromtheisolatedplateau.TheylearnRoxburyknewaboutthefateofBurtonWhite,anexplorerwhosediarytheyfind,thuspresumetobedead,insearchofdiamonds,andconfirmationofthelocaltribebeingthelethalguardiansoftheplateau'ssecrets,butalsogetsurprisinghelp...