David Innes is a mining heir who finances the experimental "iron mole," an excavating vehicle designed by his elderly inventor friend Abner Perry.

Pellucidar is inhabited by prehistoric creatures of all geological eras, and dominated by the Mahars, a species of flying reptile both intelligent and civilized, but which enslaves and preys on the local stone-age humans.

David Innes, attracted to Dian the Beautiful, defends her against the unwanted attentions of Hooja the Sly One, but due to his ignorance of local customs she assumes he wants her as a slave, not a friend or lover, and subsequently snubs him.

Rejoining Abner, he finds the latter did not even realize he was gone, and the two discover that time in Pellucidar, in the absence of objective means to measure it, is a subjective thing, experienced by different people at different rates.

Obsessed with righting the wrong he has unwittingly done Dian, David Innes escapes again and eventually finds and wins her by defeating the malevolent Jubal the Ugly One, another unwanted suitor.

Back in the world we know David meets the author, who after hearing his tale and seeing his prehistoric captive, helps him resupply and prepare the mole for the return to Pellucidar.

[2] The novel was filmed as At the Earth's Core (1976), directed by Kevin Connor and starring Doug McClure as David Innes and Peter Cushing as Abner Perry.