Sent to collect zenite to stop a plague, Kirk found the miners of Ardana in revolt against the elite city of Stratos and showed that the mine gas was dulling their minds.
In 2269 the Enterprise needed zenite from Ardana to fight a plague destroying plant life on Merak II. Ardana's elite lived in Stratos, a city floating in the clouds devoted to art and thought, while the Troglytes worked the mines below and were thought to be inferior. A group of Troglyte rebels known as the Disruptors seized the zenite.
McCoy found that zenite gas in the mines caused reduced intelligence and violent behavior, and filter masks could prevent it. Kirk forced the city leader Plasus into a mine to prove it, and the zenite was delivered. The Troglyte leader Vanna and Plasus's daughter Droxine began to understand each other.