Ned Malone and Professor Summerlee have become ill from the bites they received during the pterodactyl attack the day before. They are in considerable pain and are running high fevers, also Professor Challenger is nursing a bruised knee from the attack. Lord John is trying to further fortify the camp, after finding it had been attacked in their absence. Ned has spent the day feeling as if he is being watched, he cannot see anything, but he cannot shake the strange feeling.

That night, while everyone is asleep, a great noise arises from the area outside the camp. It is the noise of an animal being killed and another animal vocalizing its need to kill. The victor then comes after the men in the camp, but Lord John is able to frighten it away with a torch. He fears if they try to shoot it, it would either become enraged or they would end up shooting each other in their frantic attempt to kill the beast.

The next morning the men find the pieces of the dead animal strewn about the ground. The two professors feel either an allosaurus or a megalosaurus was the aggressor and the dead animal was an iguanodon. The dead animal has a circle of some black substance on its hide, which the two professors feel is asphalt.

It is also decided the men would take two hour shifts during the night to watch for predators coming near the camp. Also, Professor Summerlee begins to push Professor Challenger to find a way off the plateau. He feels they have spent enough time in the last two days exploring the island and it is now time to return home. As much as the others want to stay and explore some more, they cannot easily refute his argument that they have succeeded in their quest to prove Professor Challenger's assertion correct.

In order to expedite the process of making a map of the plateau, Ned climbs the gingko tree, which is the tallest tree on the plateau. He encounters there an ape like animal, which has a very human-looking face. He knows this is the animal which gave him the feeling of being watched.

Ned is able to climb to the very top of the tree and from there he draws a rough sketch of the plateau. He also discovers a lake they have not seen before and insists on naming it Lake Gladys, in honor of his love in England.

That night happy with himself for his accomplishment of climbing the tree and bringing back the map of the plateau, Ned decides to go for a walk. He remembers Gladys telling him, "There are heroisms all round us." So even though he is frightened, he keeps on walking further into the interior of the plateau. He checks his gun to make sure it is ready if needed, only to find he has brought the shells for the rifle, but the gun is a shotgun. It is of no use to him as a gun, but he can use it to hit something if needed.

His first discovery is the asphalt pit, where the animals became streaked with the sticky substance, he feels it is the last vestiges of the volcano which formed the plateau. He continually hears the animals in the dark forest, but he cannot see them. He comes across a large tall block of lava, which he climbs to have a better view of the land around him. He notices the black areas he thought were caves are now illuminated and concludes they must be inhabitated by a human-like species. The thought of finding humanoids on the plateau fills him with excitement.

As he is drinking water from Lake Gladys, he notices two large armadillo creatures by his feet. They are also drinking from the lake and soon they are joined by a very large deer creature and its family. All of these animals scurry away when a stegosaurus appears, to have its fill from the lake.

Ned decides he must make his way back to the camp, as it is two-thirty in the morning. He is walking back to the camp when he hears a strange growling-snorting sound coming from behind him. He hastens his pace in an effort to put as much distance between himself and whatever is making the sound. But the animal is tracking him and follows him, no matter what he does to elude it. He finally falls into a pit filled with rotting corpses of animals, while he is trying to escape the pit, he realizes it has been dug by human hands.

As he is making his way back to camp he hears a single gunshot. He thinks the others awoke to find him gone and shot the gun to help guide him back to camp. He hurries back to camp to find the others gone, the camp in shambles, the edible supplies gone, and a pool of blood on the ground. He is stunned by this turn of events.

He remembers Zambo is still waiting for the men to return, so he calls out to him for help as he needs a rope and wants to send on his letters to his editor. Zambo tells Ned one of the natives has returned and he will take Ned's letters and his request for more rope to the Indian village. Ned agrees to the plan and finishes his third letter in time for the man to take it to the village.

Ned and the others face danger from the dinosaurs, but they work out a plan to try to keep them safe. Ned makes a crude map of the plateau and takes a harrowing night time walk, from which he returns to find the others gone and a pool of blood on the ground. He feels alone and frightened, also he realizes how much he has relied on the others during this expedition.