STAR TREK: THE ORIGINAL SERIESS1, E21
The Return of the Archons
Searching Beta III for survivors of the USS Archon, Kirk and crew discover a society whose citizens appear to be staid and respectable, until the advent of "Red Hour" allows them to run amok. Kirk and Spock avoid being "absorbed" into the "body" long enough to discover the bizarre source of the planet's unity.
