One of the undisputed classic episodes of the series and franchise, regardless of whether it's one fans will have on the tip of their tongue when discussing such things (as opposed to, say, "City on the Edge of Forever"), "The Devil in the Dark" is also one of the most nuanced stories ever told by Star Trek.
The title being is one of the least-dynamic creatures physically every created. Only in reputation is the Horta any bit scary. But the thing is, it's wreaking all kinds of havoc on a Federation science team's efforts (in one of the earliest and most classic examples of the cave setting that would become a franchise staple). It's apparently just something that needs to be eliminated, and there doesn't seem to be much argument against that action.
But then Spock intervenes. There are a few iconic mind melds in Star Trek. One is in The Voyage Home, in which he learns that Gracie is pregnant. Another is in The Undiscovered Country, in which he learns exactly who is involved in the conspiracy. There's the one Sarek shares with Picard in the Next Generation episode "Sarek." And there's this one. Arguably still the most significant, most impactful. Turns the whole episode upside down.
Spock learns that the Horta is only acting out of self-preservation. That it's the good guys who are the bad guys this time. Some of this is kind of formulaic. But it's completely transcendent at the same time. It's an incredibly rare moment in the series where the moralizing goes the other way.
And yes, that makes it an iconic Spock moment, one that reverberates perhaps further than anything else the character had done to that point. It's also an episode that pivots around one scene that breathes life into the rest of the story, one that you can easily, easily recommend to anyone as a gateway into Star Trek. That's one of the definitions of being a classic. A classic will either speak directly to existing fans, or make new ones. My goal in these reviews is to separate the difference, and hopefully cross that divide.
franchise * series * essential * character