Stardate: 5818.4 --The Enterprise goes to Ardana to obtain the only known cure to a plague that threatens to decimate the vegetation on the planet Merak II. Kirk and Spock go to the cloud city of Stratos, and find out that the population is split between the Troglytes, who do the dirty work, including the mining, and the people of the city who enjoy good lives on the backs of the Troglytes. When the Troglytes rebel and threaten to stop mining, Kirk must solve the civil war to get the plague cure.

original airdate--February 28, 1969  

music: Theme song  written by Alexander Courage

Goof-- During the shot of Plasus being forcibly beamed directly to Kirk's location in the mines, the bottom of the curtains behind him change position as he transports.

Trivia-- Major plot points were inspired by Fritz Lang's classic silent film Metropolis.

Space: the final frontier. These are the voyages of the starship Enterprise. Its five-year mission: to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before.