The People That Time Forgot is a fantasy novel by American writer Edgar Rice Burroughs, the second of his Caspak trilogy.

The novel begins with the organization of an expedition to rescue Bowen J. Tyler, Lys La Rue, and the other castaways marooned on the large Antarctic island of Caprona, whose tropical interior, known to its inhabitants as Caspak, is home to prehistoric fauna of all eras.

The expedition's ship, the Toreador, locates Caprona, and while the bulk of the crew attempts to scale the encircling cliffs Billings flies over them in an aircraft.

He saves a native girl named Ajor from a large cat and a group of ape-men, and undertakes to accompany her back to her people, the fully human Galus, while she educates him in the language and mysteries of the island.

Visiting the Kro-lu village as his guest, they are parted again when Billings is attacked through the machinations of the chief Du-seen, who has designs on Ajor.

Pursued, they resign themselves to death, but are relieved by a force consisting of Bowen Tyler, Galu warriors, and the rescue crew from the Toreador, which had successfully scaled the cliffs and entered Caspak after Billings' ill-fated airplane flight.

The movie was the third and last of Amicus' Burroughs adaptations, the others being The Land That Time Forgot (1975), based on the first segment of the Caspak sequence, and At the Earth's Core (1976).