Star Trek the Original Series Episode 76 The Cloud Minders (Cribbed from Wikipedia)
On stardate 5818.4, the Federation starship Enterprise arrives at the planet Ardana on a mission to retrieve a mineral called zenite, which is needed to halt a vegetation plague on the planet Merak II. Captain Kirk wishes to speed along the negotiations for the mineral and beams down directly to the zenite mines with First Officer Spock, despite Ardana's leader High Advisor Plasus's request to beam to the floating city of Stratos.
Once Kirk and Spock arrive at the mine, they are surrounded by angry miners and a savage brawl ensues. During the struggle, Kirk notices a strange yet beautiful woman among the rioters. Plasus quickly arrives with a security force, who easily drives the rioting miners off, then invites Kirk and Spock to go with him back to the city immediately while his people search for the zenite.
Once on the floating city, Kirk and Spock are entertained as guests until the zenite can be procured from the mines. They learn that the people of Ardana are divided between the labor-class Troglytes, who work hard in the dangerous mines, while the elite city-dwellers reap all the profits and live in luxury.
A group of Troglytes, termed Disruptors by the Stratos dwellers, are rebelling against the elites. Unknown to Kirk, the city's police have captured a Troglyte who had sneaked into the city and defaced priceless artwork. Instead of divulging the leader of the rebellious workers, the man jumps to his death from a city balcony.
Plasus's daughter, Droxine, takes a liking to Spock, fascinated by his "exquisite ears", and her interest is initially returned. Another woman, Vanna seems to be interested in Captain Kirk. Vanna, however, is really the rebel leader of the Troglytes and takes Kirk hostage until the city elite meet her demands. Kirk recognizes her as the woman he saw at the mine and begins to question her, but she does not cooperate. She accuses the city-dwellers of using the Enterpriseas an intimidation tactic toward her people.
Spock, Droxine, and a sentinel arrive, and Vanna is subdued. She is then taken in for interrogation where Plasus has her tortured until she reveals the names and locations of her fellow rebels. Kirk is outraged at Plasus's actions and demands the interrogation stopped. Plasus instead orders Kirk and Spock to leave his city immediately.
The two return to the Enterprise where Chief Medical Officer Dr. McCoy reports that unprocessed zenite emits an odorless, invisible gas, which diminishes mental capacity and heightens emotion. Spock believes that the workers serving aboard the floating city have been isolated from the effects of the zenite gas. Instead of being mindless workers toiling away in the mines, they have become aware of their unfair treatment by the higher class.
Kirk has special masks made that will filter against the zenite gas and offers Plasus them for his workers; however, Plasus shows no interest. Kirk violates his ban from the city and secretly beams down to Vanna's holding cell. He explains his offer to help her and the other workers achieve equality with the city-dwellers and offers her the masks. Vanna seems interested, and Kirk overpowers a guard, whereupon Vanna and Kirk return to the zenite mines. Once there, however, she grabs Kirk's phaserand takes him hostage again with the help of two other Troglytes, Midro and Anka. The two men would rather see Kirk dead, but Vanna has other plans.
Vanna forces Kirk to experience the hardship of the miners and puts him to work digging for zenite. Vanna's men depart, leaving her alone with Kirk, who takes advantage of the situation and regains his phaser. He blasts the ceiling of the mine and seals the only way out. He then contacts the Enterprise to have Plasus found and beamed to his location.
An indignant Plasus arrives and Kirk forces him and Vanna to mine for zenite. The effects of the zenite gas become apparent as Kirk becomes more hostile. As the supply of oxygen depletes, Plasus demands to be set free, but Kirk strikes him and the two begin to brawl with mining implements. Vanna, realizing that Kirk was right about the gas after all, manages to find Kirk's communicator and signals the Enterprise to quickly beam them up before the men kill each other.
Once the effects of the gas wear off and the three settle down, Kirk offers the masks to Vanna once again. She accepts Kirk's offer in exchange for a supply of the zenite, to which Plasus strongly protests, but realizes he really has no other option. Kirk tells Plasus that the elite and miners must be treated as equal while Vanna vows that her people, who will no longer be impaired by the gas, will demand it even more vigorously now. With the supply of zenite in hand, he and Spock return to theEnterprise.