#37: Let That Be Your Last Battlefield
In case you forgot: Another legendary episode. The Enterprise finds itself mixed up in some alien race relations. Two aliens with half-black, half-white faces (one of whom is The Riddler) are running amok on the Enterprise, until Kirk solves the problem by giving them a whole planet instead.
Space racism is bad, mmkay?
But on a serious note, the Enterprise inadvertently getting itself involved in another planet's politics is a pretty solid hook, especially when not all of the aliens involve recognize the sovereignty of the Federation. This is work for diplomats, not starship captains, but Kirk does an admirable job of doing a job he hasn't be trained for.
Kirk, Scott, and Spock's initiation of the self-destruct mechanism (rather than have the Enterprise and her crew beholden to some strange alien power) is some major Hero points, though you have to wonder if they polled the rest of the crew first. "In the event this guy won't relinquish control of the Enterprise, are you willing to go down with this ship? Y/N."
The end, with Bele (The Riddler) and Lokai chasing each other for the rest of their lives, is very reminiscent of "The Alternative Factor," though made all the sadder because there is absolutely nothing to be gained by their protracted conflict. At least anti-Lazarus was sacrificing himself to save the universe.
But part of what makes this episode legendary (aside from the dopey make-up) is that the Aesop in this one is pretty hamfisted; though again, considering the timeframe when this aired, it was certainly an anvil that needed to be dropped. Sometimes it seems like it still is. The downer ending, while a powerful caution about the power of hate, does raise some uncomfortable implications for me; it seems to suggest that anything resembling a dialog or justice about race relations will only lead to civil strife and eventual doom. (No one ever explains how the Federation got to be such a post-racial Kumbaya sort of organization in TOS, and maybe you can debate that it doesn't actually exist....!) I guess I wanted to see Kirk side more heavily with Lokai and found his diplomatic neutrality kind of off-putting.