Written by Margaret Armen (based on a story by David Gerrold and Oliver Crawford) and directed by Jud Taylor, it was first broadcast on February 28, 1969.

In the episode, Captain Kirk races against time to acquire plague-fighting minerals from a world suffering from a grievous social class disparity.

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.

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 emotions.

Spock believes that Troglytes serving aboard the floating city have been spared the effects of the gas, enabling them to organize the rebellion.

Club gave the episode a 'C+' rating, noting that it "had enough story that it didn't drag too terribly near the end" but that "philosophy-wise, it chickened out in a way that's highly unusual for the show".

"[3] This episode was released in Japan on December 21, 1993 as part of the complete season 3 LaserDisc set, Star Trek: Original Series log.3.