The Man Trap
09/08/66 -- Stardate: 1531.1
In the form of archeologist Robert Crater, a creature that needs salt to survive beams aboard the Enterprise and begins killing crew members for the salt in their bodies.
09/15/66 -- Stardate: 1533.6
Seventeen year old Charlie Evans, last survivor of a colony on Thasus, is rescued by the Enterprise and begins causing trouble with his psychic powers.
Where No Man Has Gone Before (Second Pilot)
09/22/66 -- Stardate: 1312.4
The Enterprise encounters a force field at the edge of the galaxythat intensifies the latent psychic powers of Lt. Commander Gary Mitchell and Dr. Elizabeth Dehner.
The Naked Time
09/29/66 -- Stardate: 1704.2
On the planet Psi 2000, a rescue team picks up a virus that removes the crew members' inhibitions, causing chaos on the Enterprise.
The Enemy Within
10/06/66 -- Stardate: 1672.1
A transporter malfunction splits Kirk into his two inate halves -- one good but weak-willed and the other evil.
10/13/66 -- Stardate: 1329.1
Interstellar smuggler Harry Mudd is brought aboard the Enterprise with three women who get their beauty from an illegal drug given to them by Mudd.
What Are Little Girls Made Of?
10/20/66 -- Stardate: 2712.4
In search of exobiologist Dr. Roger Kirby, Nurse Chapel's ex-fiancee, the Enterprise finds that he has constructed androids and given himself an android body in a plan to replace key Federation leaders with android duplicates.
10/27/66 -- Stardate: 2713.5
The Enterprise encounters an Earth-like planet where a virus has killed all of the adults by causing them to age rapidly, while the aging process in children is slowed.
Dagger of the Mind
11/03/66 -- Stardate: 2715.1
A maniac who escapes from the Tantalus V penal colony uses a brainwashing device in an attempt to gain control of the Enterprise.
The Corbomite Maneuver
11/10/66 -- Stardate: 1512.2
The Enterprise encounters the evil-looking Balok and his huge spherical ship, the Fesarius, but later discover that Balok is really a small, friendly alien who has been testing the Enterprise crew.
The Menagerie (Part 1)
11/17/66 -- Stardate: 3012.4
Spock commandeers the Enterprise to take Captain Christopher Pike to the off-limits planet Talos IV.
The Menagerie (Part 2)
11/24/66 -- Stardate: 3012.5
Enroute to Talos IV with Captain Pike, Spock faces a court-martial, during which the story of the first contact with the Talosians (see The Cage) is revealed.
The Conscience of the King
12/08/66 -- Stardate: 2817.6
The Enterprise crew discovers that the leader of a traveling theater group is really Kodos the Executioner, who murdered most of the population of Tarsus IV 20 years earlier.
Balance of Terror
12/15/66 -- Stardate: 1709.1
A Romulan Bird of Prey attacks the Federation outposts near the Neutral Zone, starting a cat-and-mouse confrontation with the Enterprise.
12/28/66 -- Stardate: 3025.3
The Enterprise crew takes shore leave on a planet where their thoughts are brought to life by underground machinery of an advanced race.
The Galileo Seven
01/05/67 -- Stardate: 2821.5
The shuttlecraft Galileo and its seven occupants crash-land on a hostile planet, and Spock must assume command to give them a chance at being rescued.
The Squire of Gothos
01/12/67 -- Stardate: 2124.5
Four Enterprise crew members are kidnapped by Trelane, an arrogant, impetuous alien who turns out to be a child using the crew members as play things.
01/19/67 -- Stardate: 3045.6
After chasing a Gorn ship into an uncharted sector of space, Kirk and the Gorn commander are transported to a desert planet, where they are forced to duel to the death.
Tomorrow Is Yesterday
01/26/67 -- Stardate: 3113.2
The Enterprise is thrown back in time to 20th Century Earth after a close encounter with a black star, and is reported as a UFO by an Air Force pilot.
02/02/67 -- Stardate: 2947.3
Kirk is charged with negligence in the death of an Enterprise creman, but is later acquitted when Spock discovers that the crewman isn't really dead.
The Return of the Archons
02/09/67 -- Stardate: 3156.2
The Enterprise crew beams down to a planet where the zombie-like inhabitants are controlled by a super computer known as Landru.
02/16/67 -- Stardate: 3141.9
The Enterprise finds the S.S. Botany Bay, a 1990's sleeper ship carrying a group of genetically bred supermen led by Khan Noonian Singh.
A Taste of Armageddon
02/23/67 -- Stardate: 3192.1
After the Enterprise is declared a victim of an interplanetary war fought only in the memory banks of opposing computers, Kirk and Spock force the warring planets to face the destruction of real war or settle their dispute.
This Side of Paradise
03/02/67 -- Stardate: 3417.3
All of the Enterprise crew, except Captain Kirk, are exposed to spores that induce a feeling of euphoria and a desire to remain on the planet.
The Devil in the Dark
03/09/67 -- Stardate: 3916.1
A mining colony on Janus VI is faced with death and destruction caused by a rock-like creature, the Horta, which turns out to be a mother trying to protect her eggs from the miners' equipment.
Errand of Mercy
03/23/67 -- Stardate: 3198.4
The Organians intervene in a conflict between the Federation and the Klingons by imposing a peace treaty that will be enforced by the power of the Organians' minds.
The Alternative Factor
03/30/67 -- Stardate: 3087.6
The Enterprise finds Lazarus on a deserted planet, and soon discovers that he is in a life-and-death struggle with an evil duplicate from a parallel anti-matter universe.
The City on the Edge of Forever
04/06/67 -- Stardate: 3134.0
After an accidental overdose of the stimulant cordazine, Dr. McCoy jumps through a time portal on a deserted planet and ends up on Earth in the 1930's.
04/13/67 -- Stardate: 3287.2
While investigating the death of Kirk's brother and other colonists on Deneva, Spock is attacked by a flying creature that attaches itself to its victim's nervous system.