Story By: Gene Roddenberry
Writer: Boris Sobelman
Director: Joseph Pevney

Captain Kirk: William Shatner
Science Officer, First Officer, Cmdr. Spock: Leonard Nimoy
Dr. Leonard "Bones" Mc Coy: DeForest Kelly
Lt. Sulu: George Takei
Lieutenant Commander Montgomery Scott: James Doohan
Lieutenant Uhura: Nichelle Nichols

Landru: Charles Macaulay
First Lawgiver: Sid Haig
Reger: Harry Townes
Tamar: Jon Lormer
Hacom: Morgan Farley
Marplon: Torin Thatcher
Tula: Brioni Farrell
Lindstrom: Christopher Held
Lt. O'Neil: Sean Morgan
Bilar: Ralph Maurer
Guard: David L. Ross
Yeoman Tamura: Miko Mayama

Stardate 3156.2

The U.S.S. Archon disappeared on Beta III in Star system 6-11, a century ago. Now the Enterprise orbits the planet and some of the crew beam down trying to find anything about the Archon. Down at the planet Sulu is hit by a beam and back on board it is obvious that he is under the influence of a controlling power. Kirk, Spock, and others make contact with the people of the planet and Spock is introduced as a "stranger from the hills". They are guests of Reger and his daughter Tula. 

All people on the planet seem to hide something, are monotone, just functioning and nobody seems to speak freely, though everybody is extremely peaceful. Later they learn that the entire culture is controlled by a group of 'lawgivers', who in return are controlled by "Landru". Landru seems to be present everywhere and all the time. And everybody fears him. All strangers are absorbed by "the body" and become part of the system. Now the Enterprise people know what happened to the crew of the U.S.S. Archon. Some Archon survivors, Reger and Marplon, have formed an underground movement to resist the Body. Kirk, Spock, Lindstrom a. o. spend a night at the place (Spock seemingly sleeping with open eyes). 

The next day they experience the "Red Hour", that is a twelve hours madness where everybody attacks everybody in order to kill the other. This is to relieve pressure and prevent over–population. Kirk and Spock are found not to have taken part in the "Red Hour" and are arrested. Their fate is to be imparted into the culture. They try to escape, but are caught in the attempt. McCoy is taken away and, when he's brought back, he shows the same behaviour of the natives - he has been absorbed. Kirk is also put into the manipulating device – and shows the same glance and behaviour of the other people. Spock is put in next and discovers that the machine is operated by people of the underground – making sure the treatment is ineffective to them, unfortunately they didn't step in time to spare the doctor, but they succeeded with Kirk, whose tamed attitude was faked. 

The rebels help Kirk and Spock to reach Landru. The image shown of Landru turns out to be a projection by a sophisticated computer built by Landru, a scientist who lived 6,000 years before. He had wanted to eliminate wars and fighting. The computer was programmed with his scientific thoughts and memories, but not with his wisdom. Independent thoughts were not allowed and everybody was controlled. Kirk convinces the computer that he has harmed the people instead of helping them. This causes Landru to destroy itself. Now the people can learn to think by themselves and, when the crew is back on board, Kirk contacts the Federation to send help to Beta III.