Upon beaming down to the planet Gideon, Kirk finds himself on a duplicate of the Enterprise, where he meets a woman named Odona (Sharon Acker) who yearns for a chance to live far away from her vastly overpopulated world—a world where no one dies.
The subject of the story is overpopulation and the need for extreme measures to combat the problem, as the Gideons hope to introduce into the population a rare disease carried by Kirk, allowing their people to age and die as they once did centuries ago. Unfortunately, the plot tackles its message in such a roundabout way that it's hard to swallow a lot of it. For one, I find it highly unlikely that the Gideons would build an exact duplicate of the Enterprise just to fool Kirk into helping them—an approach they should know is destined to fail.
Then comes the idea of billions of people literally piled up together upon each other because of overpopulation, which strikes me as somehow implausible. (How does anything in society function given this sort of problem? The idea of urgent overpopulation is fine, but the absurdity of showing crowds of people unable to move is simply unnecessary.) There's also far too much time spent on the plots where Kirk ponders the nature of being on an empty Enterprise while Spock attempts to locate the captain ... although I somewhat enjoyed the contest of semantics between Spock and Gideon Prime Minister Hodin (David Hurst).
It's a watchable episode, but there are too many dubious ideas, and the moral questions are not presented in a way that allows any realistic debate or analysis. There's a much better story lurking beneath some of the concepts inefficiently jammed together here.