Ned and the others are enjoying living in a camp near the Accala's, but independent from them. The Accalas consider the men a sort of good luck charm, so they refuse to help them find a way off the plateau. The only one who is willing to help is Maretas, the chief's son, who they helped rescue.

The men have made some more discoveries in their additional time there, for instance they now know the Accalas keep iguanodons in a way that is reminiscent of how we keep cattle. They have also learned the caves, in which the Accala live, have drawings of all the animals on the plateau on their walls. If for some reason all the living beings on the plateau should cease to exist, a record of them will still survive on the walls of the caves.

The tribe is terrorized one day by huge frog like beings, which are impervious to bullets. These two dinosaurs would simply fall on their victims, crushing them with the weight of their bodies. The only way they are eventually stopped is by being pelleted with poision-dipped arrows, which the Accala shoot at them.

The members of the expedition also encountered ichthyosaurus, deadly water snakes, and a phororachus just to name a few of the dinosaurs they see or are pursued by. They are able to kill some to take back as proof of their findings.

Sir John is still interested in the pterodactyls and has built himself a protective cage to wear when he is near their rookery. Ned cannot understand his fascination with the creatures.

Challenger, who has been working on a method of escape, finally shows the others his idea. He has rigged up a type of balloon using the gas from the mud geyser and a dried stomach from a fish lizard, by putting a harness around it, he can control the balloon. His intention is to use it as a type of hot air balloon to bring the men, one by one, back down to the surface. Professor Summerlee is not excited about the idea of being a passenger on such a conveyance.

But before they can get very far with this plan, Maretas brings Ned a piece of bark with a crude map on it. It shows the storage caves and marks one as special point of interest to the men. The men decide to explore it and after a misstep, eventually find the right passage out of the side of the plateau. The next night, after gathering their belongings, the men make their escape.

They return to the civilized world and find great excitement about their journey and discovery. They did not know the rest of the world has been aware of their exploits. The men are scheduled to give a report to the Zoological Institute, which has to be moved from the Zoological Hall to Queen's Hall, because of the number of people who want to be in attendance.

Professor Summerlee gives an accounting of their adventures, leaving out the exact location of the plateau and the shooting death of the native guide. At the end Dr. James Illingworth of Edinburgh, stands up and asks to be allowed to make an amendment to the proceedings. He calls into question the veracity of the report. He insinuates the men may have embellished their findings to gain notoriety.

The general feeling of the audience is this man should sit down and be quiet. Some others are on his side, but Professor Challenger takes the matter into his own hands. He talks about the insects they have brought back and the pictures they have in their possession, both of which are decried by the audience. He then brings out his secret piece of evidence, a baby pterodactyl.

The audience goes wild at the sight of the frightening creature, so much so that they in turn frighten the creature. It takes flight and flies around the hall, eventually escaping through an open window.

This last piece of evidence convinces the naysayers and the audience hoists the four men upon their shoulders and carry them through the streets. The parade lasts until midnight, when the men are once again allowed to go into Lord John's rooms at the Albany.

The pterodactyl is spotted several times, the last by a ship at sea. It is presumed it died at sea as it tried to return home.

Ned returns to Gladys's home to claim his bride, but unfortunately, she has in his absence become the wife of another man. This man is not a man of adventure, but instead he is a law clerk. Ned is saddened by the news, but he soon rallies from this set back.

One night as the four men are gathered together in Lord John's rooms, Lord John tells them the reason he was so interested in the blue clay at the volcanic pit. He had seen similar clay only one other place, the De Beers Diamond Mine of Kimberley and that is why he was eager to explore amongst the pterodactyls. He did find diamonds there, and was able to bring home a substantial amount of them, which he shared with the others.

Challenger is going to open a private museum with his share of the money. Professor Summerlee is going to retire from teaching so he can classify chalk fossils and Lord John is going to mount another expedition to the plateau. Ned has decided, since Gladys is married, that he will join Lord John in exploring the plateau.

The men return home to great excitement and some criticism. Challenger silences the skeptics by producing a live dinosaur and Ned is saddened to learn Gladys has married. The men are happy to find out about the windfall of money coming their way, because of Lord John's diamond find. They all return from their adventures changed men, who will never look at the world in the same way as they did before.