Somehow, in spite of all my reading of Star Trek reviews, the Star Trek Chronology, and the like, I managed to stay insulated from what happens in "The Mark of Gideon," so I was able to enjoy seeing it without any real expectations - without knowing what was really going on. That alone made it enjoyable, as these days it is increasingly hard to find unfamiliar Trek.
The story starts with a great twilight zone feel as Kirk finds himself all alone on the Enterprise. Is it a parallel universe, a temporal anomaly, some elaborate alien deception? (Of course, it turns out to be the latter.)
Spock's struggle to get permission to rescue the captain is also well played out. His intense loyalty to Kirk leads him to fight against the Federation, Starfleet, and the Gideon Prime Minister Hodin. The diplomatic sparring with Hodin is especially interesting to watch.
And what is the point of this elaborate alien deception? Why, the planet is horribly overpopulated because the inhabitants have become all but immortal, and they what to extract a deadly illness from Kirk's blood to thin out the herd. Unfortunately this premise - and the Gideons solution - suffer in part from a lack of plausibility, but much more so from a lack of explanation.
I have already commented at length on the idea that aging is not a biological necessity as it relates to the Drayan in the Voyager episode "Innocence." But like the episode "Innocence," it seems like too much time is spent on the build up to revealing the Big Secret, and not enough time is spent helping us believe this is actually happening.
There's also some internal inconsistency in that Hodin looks much older than his daughter Odona. But if these people don't age, then shouldn't they look to be about the same age? That would have made the revelation that Odona is his daughter genuinely surprising and would elevate the portrayal of these very human looking aliens to something truly alien.
And if this culture has the resources to create a flawless replica of the Enterprise, wouldn't they have the resources to . . . well, fill in the blank? For example, why haven't they expanded their population to other planets? Perhaps it is an idea that runs counter to their deeply ingrained culture of isolationism. But since we don't get to really understand their culture the answer to that question remains ambiguous.
I doubt the term "ecological footprint" had been coined when the episode first aired, but it is hard to accept the idea that a planet could support people shoulder to shoulder from sea to sea without suffering a complete ecological collapse of its life systems. Even if this is left unexplained it would be worthy of some throwaway line. McCoy says, "I wonder how a planet could even support so many people?"
In fact, I wonder if the episode could have been stronger had McCoy been the focus of the story. What if the Gideons had requested a Starfleet doctor to assist them with developing an inoculation against some deadly disease(s). McCoy arrives with equipment and medical samples, only to make the horrifying discovery that they are not inoculating people against a plague, they are try to create one. But are they murdering their own people, or are they are combating a cancerous growth problem? The ethical debate is on, and you can be sure that McCoy would have plenty of fiery things to say about it. (Of course the down side of this approach is we don't get to see Kirk running around with another space-babe-in-pajamas, but certainly we've seen enough of this already.)
Perhaps the episodes greatest weakness is that it simply never settles on any one concept to explore. There are some great concepts directly or indirectly brought up in this story: agelessness, overpopulation, euthanasia, what it really means to respect life, Kirk's readiness to advocate not only contraception, but government organized sterilization. There could be a great episode about any one of these issues, but in the end too much time is spent on the effectively eerie, but ultimately irrelevant puzzle of the duplicate Enterprise. (Where did they have room for such a huge structure anyways? Underground I suppose.)
Whatever the shortcomings, I will say this - the glimpse of Gideon's population outside the council chamber is a chilling portrayal of a future civilization gone wrong. In some strange way it reminds me of something out of the movie Logan's Run. These people in simple, one-color suits, pushing and shoving past each other in sickly green light - it's really very creepy, and very claustrophobic. It may not make sense under scrutiny, but it's an effective visual metaphor for the problem of extreme overpopulation.
And if we accept the premise for a moment, there is something striking about the question of whether Hodin is a heartless father who uses his daughter as a guinea pig in a lethal experiment, or a selfless father who lets his daughter choose to make the ultimate sacrifice for her people.
So somehow "The Mark of Gideon" manages to rise above it's own shortcomings to be a good story, and to suggest that with a couple more drafts there could even have been a truly great story here.