The Federation starship Enterprise arrives at the planet Ardana to take on a shipment of zenite, needed elsewhere to halt a botanical plague. Captain Kirk and First Officer Spock beam directly to the zenite mines, where a group of miners, led by a young woman, attempt to take them hostage. High Advisor Plasus arrives with a security force, driving the miners off, and invites Kirk and Spock to return with him to the floating city of Stratos. Kirk and Spock are entertained as guests until the zenite can be recovered. They learn Ardanan society is divided between the Troglytes, who perform all physical labor, and city-dwellers who live in luxury. A group of Troglytes known as the Disruptors are rebelling against the elites.