Edward Malone, a young reporter for the Daily Gazette, asks his editor for a dangerous assignment to impress the woman he loves, Gladys, who wishes for a great man capable of brave deeds and actions. His task is to approach the notorious Professor Challenger, who dislikes the popular press intensely and physically assaults intrusive journalists. The subject is to be his recent South American expedition which, surrounded by controversy, guarantees a hostile reaction. As a direct approach would be instantly rebuffed, Malone instead masquerades as an earnest student. On meeting the professor he is startled by his overwhelming intellect - his intimidating physique too - but believes his ruse is succeeding. Seeing through the masquerade, then confirming Malone's scientific knowledge is non-existent, Challenger erupts in anger and forcibly throws him out. Malone earns his respect by refusing to press charges with a policeman who saw his violent ejection into the street. Challenger ushers him back inside and, extracting promises of confidentiality, eventually reveals he has discovered living dinosaurs in South America, following up an expedition by a now-deceased previous American explorer named Maple White. At a tumultuous public meeting in which Challenger experiences further ridicule (most notably from a professional rival, Professor Summerlee), Malone volunteers for an expedition to verify the discoveries. His companions are to be Professor Summerlee, and Lord John Roxton, an adventurer who helped end slavery on the Amazon; the notches on his rifle showing how many slavers he killed doing so.Running the gauntlet of hostile tribes, the expedition finally reaches the lost world with the aid of Indian guides, who are superstitiously scared of the area. Summerlee retains his scepticism - although being delighted at making other scientific discoveries in the field of botany and entomology: even a glimpse of a pterodactyl at a distance fails to convince him, believing it is some species of stork (the sharper-eyed Roxton is inclined to agree it is not a stork but has no clue what it really is), until a night-time encounter when it flies down and is seen by all at close range, as it steals the companions' dinner. After this, Summerlee apologises to Challenger. The cliffs to the plateau itself prove to be apparently unscalable, but an adjacent pinnacle turns out to be climbable, and moreover, has a tall tree which can be cut down and used as a bridge, which allows the four explorers to cross to the plateau. However, they are almost immediately trapped on it, thanks to the treachery of one of their luggage-porters, Gomez: who, as it turns out, is a former slaver whose brother had previously been killed by Roxton during his anti-slavery activities. Gomez takes his revenge by dropping the tree off the cliff, stranding the explorers on the plateau. Gomez himself is subsequently killed by another porter, a negro ex-slave named Zambo, who remains loyal to the party: but the latter is unable to do much more to help, other than send some of the company's supplies over by rope.