This is yet another fine example of intelligent writing, and superb acting and execution, definitely classic Dr. Who material. Even though all visuals for this episode are gone, the audio track survives, and with the fabulous linking narration by Peter Purves, it works extremely well to hear what is transpiring.
The Doctor, Steven, and Dodo arrive on an unknown planet in the far distant future, where they encounter two separate human societies, on the surface one seems to be savage throwbacks to an archaic and primitive time, the other, a highly sophisticated, rational, civilized society, a society that were expecting the Doctor's arrival. But soon it is revealed that these seemingly civilized people are exploiting the savage people that live outside of the city complex, capturing each one and extracting their life energies, and then transferring that energy into themselves. These so-called civilized people demonstrate a utilitarian viewpoint, that what they do is for the good of their people, that the good they do outweighs the harm they inflict on those who exist outside their society. One extraordinary moment that is quite remarkable is when Jano absorbs some of the Doctor's life force into himself and soon begins to unexpectedly exhibit the good Doctor's mannerisms, even going so far as to talk exactly like him, almost as if suffering from a split personality. as these extreme traits fade, Jano retains a sense of justice and of right and wrong, which allows him to assist the Doctor, Dodo, Steven and the Savages to storm the city complex and destroy the energy transfer equipment. this story is very unique as it is another demonstration of how surface appearances cannot be used as a perception of how people seem to be. excellent performances all around. this story also marks the departure of a very wonderful travelling companion, Steven Taylor, who remains behind to lead and unify the people. definitely a must have.