The U.S.S. Enterprise is investigating Beta III, where the U.S.S. Archon disappeared over 100 years before.
When the landing party exhibits strange behavior, Kirk sends another party down to investigate. They find the culture on Beta III is quiescent, with no creative tendencies (Meaning the Brother hood of Jehovah’s Witness). The entire culture is controlled by a group of 'lawgivers' (The Elder Body of Jehovah’s Witness’s) known as "The Body" which is, in turn, controlled by the omniscient Landru. (The Governing Body of Jehovah’s Witness’s over in Bethel) The inhabitants change from normal, peaceful people to a illogical unreasoning mob at the coming of the Red Hour ( Meaning after the Circuit and District assemblies). This 'Festival' is the society's only outlet for the tyrannical hold that Landru (The Governing Body of Jehovahs Witness's) has over them at all other times.
Meanwhile, the U.S.S. Enterprise (peace loving decent brothers and sisters who are not afraid to say why! or NO WAY!) is being pulled from its orbit, its crew is to be absorbed into the Body (The elder body’s manipulating control of their lives). This, they discover, is what happened to the U.S.S. Archon, so many years before and hense they have become like Zombies. Archon survivors from this mind control have formed an underground of sorts to fight the Body, (Witness Elder Body) and they help Kirk and Spock reach Landru (The Governing Body of Jehovah’s Witness’s). Landru turns out to be an incredibly complex computer built by Landru, a scientist who lived 6,000 years before, who wanted to guide his people into a peaceful, civilized society with out thought control. (The Bible Students, before Judge Rutherford did his hostile take over). Landru had affected the computer with his scientific thoughts and memories, but not his wisdom. For centuries the computer, 'Landru,' (Modern day Jehovah's Witness's as represented by the Governing Body located in what they call Bethel) has been interpreting his suggestions to the point that no one is allowed independent thought (Which has taken mans God given conscious away and replaced it with mans which hinders man and women's ability to worship him properly). Kirk tells the computer that instead of helping to nurture the culture of Beta III, it has harmed it. Landru destroys itself, (because of the unrelenting Total Logic of many ex-Jehovah's Witness's Internet Web Sites) leaving the Betans to work towards the sort of culture Landru had originally wanted so many centuries before. With the promise of Federation help on the way, Kirk and his crew beam back to the U.S.S. Enterprise.