Lord John, Professor Challenger, Professor Summerlee and Ned Malone have reached the bottom of the plateau. The problem they face is how to scale the cliffs which surround it, in order to gain entry onto the plateau. The men spend several days working their way around the base looking for an area that is scalable.

The first thing they encounter, as they survey the plateau's base, is the camp which was set up by Maple White. It includes, among other things, a sign attached to the base of a tree, which points out the direction he followed to enter the plateau. As they follow the direction of the sign the men encounter a patch of tall bamboo and Ned discovers the remains of a man. They decide he must have been traveling with Maple White, because of the sheds of European clothing found on the skeleton and a watch with the initials J.C. on it. Challenger tells the others he spoke with a priest, who had met Maple White and he confirmed Maple White was traveling with a man named James Clover.

The men find arrows drawn in white chalk at various spots around the base. They finally find an arrow inside a narrow cleft of a rock face that points up. They order the natives traveling with them to pitch a camp and they go inside the cleft to explore it. Finding nothing the men are discouraged, until Lord John notices a cave opening above their heads in the cleft. The men climb into the cave and follow it until they are stopped, by an area which has been obstructed by a rock slide. Even though they are discouraged, the men decide to continue with their exploration of the cliffs.

That night they kill a pig-like animal to eat for supper and as they are cooking it a pterodactyl swoops down over their heads, taking the animal for its supper. This occurrence causes Professor Summerlee to apologize to Professor Challenger for his skepticism of Challenger's claims. Following this incident, the two men become friends and allies.

It takes them six days to finish exploring the circumference of the plateau, all the time looking for a place to climb up the cliffs and enter it. At the end of their exploration, they have found no way to access the place they had traveled so far to see.

The men are very discouraged by this outcome and go to bed feeling as if their trip has been for nothing. The next morning Challenger is full of hope and tells the others he has solved their problem. He has them scale the pinnacle they saw upon reaching the plateau area, even though there is a wide space between it and the surface of the plateau. After they all reach the top, they discover the beech tree they had been using to anchor themselves to the top of the pinnacle, could also be used to bridge the gap.

Ned and Lord John cut down the tree and Lord John makes sure they are armed before they try to cross the bridge. This is because during the exploration of the cave a bolder came crashing down at the men. They decided it could have killed them and a person must have rolled the stone. Because of this, they are now taking precautions before entering the plateau. As part of these precautions, they have two of the natives scale the precipice to help defend them. The men all make it safely over the bridge, but soon after the tree bridge is pushed down into the gap by Gomez, one of the native guides. He is avenging the death of his brother by Lord John. Lord John retaliates to this act by killing Gomez.

Zamo, another one of the guides, stays loyal to the men and provides them with provisions. He also promises to stay nearby to help them in any way he can.

The next day the men begin to cautiously explore their new home. They first find a place to make a kind of fort, a campsite protected by thorny plants and trees under some rocks for protection. Zamo is still there providing the men with the provisions they so desperately need.

They decide to name their campsite Fort Challenger and the plateau Maple White Land. These names honor Professor Challenger and Maple White, the discoverer of the plateau.

They see a family of iguanodons as they are walking through the plateau. After watching them for a while they stumble upon a volcanic pit, which is a breeding place (rookery) for pterodactyls. All is going well as they observe these dinosaurs in their natural habitat, until Lord John decides to look over the edge of the pit.

The male pterodactyls spot him and attack the men in an attempt to kill them. It is only through the use of Lord John's elephant gun and quickly running to the shelter of a wood that the men escape. Upon returning home, they have found that some animal has gained entry to their camp, by using the branches of a tree, and ruined some of their supplies.

At the end of the day Lord John is fascinated by the color of the clay in the volcanic pit, because the clay was blue. Ned has no idea what the significance of blue clay is, but he is curious.

The men experience the wonder of seeing living dinosaurs in and around the plateau. They also are stranded on the plateau, because Gomez is seeking revenge for the death of his brother. The men are all learning to cooperate in order to survive their unusual circumstance.