The U.S.S. Enterprise comes to the planet Ardana to acquire zienite, a rare mineral needed to stop a planet-wide plague on Merak II. The zienite is not available, however, because the miner class Troglytes are rebelling against the rulers of Ardana, who live in the cloud-city of Stratos. The Stratos-dwellers insist that the Troglytes are naturally inferior beings, but Kirk discovers that the Troglytes are being affected by a gas emitted during mining.

James Doohan (Lt. Cmdr. Montgomery Scott)
Jeff Corey (Plasus)
Diana Ewing (Droxine)
Charlene Polite (Vanna)
Nichelle Nichols (Lt. Uhura)
Kirk Raymone (Cloud Guard #1)
Jimmy Fields (Cloud Guard #2)
Fred Williamson (Anka)
Garth Pillsbury (Prisoner)
Harv Selsby (Guard)
Ed Long (Midro)