When Kirk must obtain zenite to cure a deadly plague, the Enterprise stops at the planet Ardana, which is divided into two societal units—the Stratoses, artists and scholars who live in the city high in the clouds, and the Troglytes, who do all the hard labor in the mines below. Unfortunately, the political turmoil is making it difficult for Kirk and Spock to obtain the zenite. And Kirk draws the line when Plasus (Jeff Corey), the arrogant leader of Stratos, ops to employ torture on a Troglyte dissident named Vanna (Charlene Polite) as an attempt to get the zenite from her.
"Cloud Minders" is a good realization of a classic TOS idea, in which Kirk's steadfast humanism leads him to intervene in a culture's governmental operations, whether they want his help or not. There's something satisfying about seeing the wrongs of a society set right ... even if we really don't have much business in interfering (though that issue itself is confusing because the episode doesn't seem sure whether Ardana is a Federation planet bound by its values). By making everyone else in the plot hard-headed adversaries, this episode does a good job of manipulating us into feeling that Kirk has every right to impose his beliefs on others.
The resolution is idealistic to the point of shallowness (centuries of exploitation fixed within a few mere hours), but the story executes well enough that I don't care. After so many dismal third-season offerings, it's nice to see a conflict that has some fire and attitude injected into the confrontations.