The TARDIS materialises in what the Doctor claims is a time of great peace and prosperity – but if the Elders of the city are so wise and powerful why do savages still live in the wilderness outside the city walls? And why do the people of the city apparently hunt and harvest the savages? The Doctor learns that all of the Elders' great achievements are based on a terrible form of exploitation; the people of the city are harvesting the life essence of the savages, reducing them to little more than cattle and devastating their civilisation while the Elders prosper. When the Doctor vows to put an end to this, the leader of the Elders, Jano, has him sent to the laboratories – but Jano, unwilling to risk the life essence of an alien on any of his people, takes it all into himself, and thus acquires the Doctor's morals and ethics as well. With Jano's help, the Doctor, Steven and Dodo organise the savages and help them strike back against the cruel Elders. They will require a strong leader to guide them, however, and they choose Steven, who leaves the Doctor's company to lead the newly united people.