When the TARDIS materializes on an alien planet, the Doctor insists that he and his companions have arrived in the far future. Steven and Dodo think otherwise, however, after they encounter a band of cave-dwelling primitives who are terrified of strangers. The travelers soon discover that the planet’s population is divided into two castes, and that the professed idyll of the Elders – who inhabit a technologically advanced city – seems oddly dependent upon the unsophisticated savages.