Episode: 001 | Aired: September 08, 1966
Doctor Leonard Bones McCoy reconnects with Nancy Crater, a former girlfriend, when the Enterprise brings supplies to an archeological survey group on the planet M-113, but Nancy harbors a lethal secret.
Episode: 002 | Aired: September 15, 1966
Teenaged Charlie Evans, who has been raised from the age of 3 by non-corporeal beings, is transferred to the Enterprise. Dangerously unable to control the tremendous psionic abilities given to him by the Thasians, Charlie finds it impossible to function in normal human society.
Episode: 003 | Aired: September 22, 1966
While patrolling the outer boundary of the galaxy, The Enterprise encounters an energy field that mutates Kirks close friend Lieutenant Commander Gary Mitchell into a superhuman. When Mitchell becomes dangerous, Spock believes his death is the only solution. Kirk exiles him to an uninhabited planet, but Mitchell is too strong to be held captive and escapes.
Episode: 004 | Aired: September 29, 1966
During the investigation of the disintegrating planet Psi 2000, the Enterprise is contaminated by an alien virus that causes a complete lack of inhibitions. Social order breaks down, and the crew exposes their innermost feelings. In a heart wrenching development, Nurse Christine Chapel professes her love for Spock, who has become deeply emotional under the influence of the virus. Kirk, paranoid and anxious, is unable to command, while the Enterprise orbits around the doomed Psi 2000.
Episode: 005 | Aired: October 06, 1966
A malfunction in the transporter splits Kirk into two alter-egos, each with half of his personality. The dark side of Kirk is violent, while his light side is compassionate. McCoy and Spock work to fuse the two Kirks back into a single person, while a landing party, led by Sulu, is stranded on the surface of a freezing planet until the transporter can be repaired.
Episode: 006 | Aired: October 13, 1966
Wanted criminal Harry Mudd and his cargo of three beautiful women are beamed aboard the Enterprise as his ship is being destroyed in an asteroid field. The Enterprise burns out its dilithium crystals during the rescue, and heads quickly to a mining planet to replenish the supply. Mudd makes advance contact with the miners and strikes a deal hell give them the women in exchange for his freedom.
Episode: 007 | Aired: October 20, 1966
Dr. Roger Korby, the Pasteur of archeological medicine, and the long-lost fianc of Nurse Christine Chapel, is discovered on planet Exo III. Korby has used ancient machines left behind by the Exoites to create android aides, but his plans, and his secrets, go far beyond his robotic companions.
Episode: 008 | Aired: October 27, 1966
The Enterprise answers an old distress signal from an unnamed planet and discovers that 300 years before, a disastrous biological experiment was performed there. The experiment created a virus that killed adults and slowed the natural aging process of children, leaving them in a state of pre-pubescence for centuries. The landing party contracts the virus, except for Spock, who becomes a carrier.
Episode: 009 | Aired: November 03, 1966
While investigating a revolutionary treatment for the criminally insane that is being performed at the Tantalus Penal Colony, The Enterprise discovers a chilling exercise in mind control. Dr. Tristan Adams, director of the Colony, has been using a neural neutralizer to control not only the inmates, but his staff as well.
Episode: 010 | Aired: November 10, 1966
The Enterprise is captured by a powerful spaceship and threatened with destruction by its sinister captain, the frightening Balok. To save the ship, Kirk stages a desperate bluff, telling Balok that if the Enterprise is fired upon, the corbomite in the starship's hull will self-destruct and destroy both ships.
Episode: 011 | Aired: November 17, 1966
A call sent from Captain Christopher Pike, the former captain of the Enterprise and Spocks old commander diverts the Enterprise to Starbase 11. Pike, completely paralyzed, is abducted by Spock and brought aboard. Captain Kirk discovers that Spock has hijacked the ship, setting the controls on a course for the forbidden planet Talos IV. To visit this planet is an offense punishable by the death penalty, and Kirk has to convene a court-martial against him.
Episode: 012 | Aired: November 24, 1966
Spocks court-martial proceedings reveal the story of Captain Pikes previous visit to Talos IV, during which the Talosians beings with the ability to create powerful illusions of the mind attempted to breed Pike with women they provided to him. As the proceedings draw to a close, it is revealed that the court-martial is meaningless, an illusion created by the Talosians for Kirk's benefit.
Episode: 013 | Aired: December 08, 1966
James Kirk, Lt. Kevin Riley and Dr. Thomas Leighton are the only remaining survivors of crimes of mass-murder committed by "Kodos the Executioner" on Tarsus IV many years ago; others who might bear witness have been killed in mysterious accidents. Leighton contacts Kirk and tries to persuade him that Kodos is still alive and living under an assumed identity, that of Anton Karidian, an actor with a traveling theater troupe.
Episode: 014 | Aired: December 15, 1966
A Romulan warbird attacks and destroys Outpost 4, which guards the Neutral Zone between Federation and Romulan space. The Enterprise gives chase, and is able pick up a visual from the Romulan Bridge, revealing that Romulans look very much like Vulcans. This inflames the prejudice of Lieutenant Andrew Stiles, whose family fought in the Romulan wars, and he instantly becomes suspicious of Spock.
Episode: 015 | Aired: December 29, 1966
The Enterprise visits a mysterious planet where dreams come true and thoughts become reality. At first amusing, the results of the crews fantasies take a deadly turn.
Episode: 016 | Aired: January 05, 1967
The shuttlecraft Galileo, piloted by Spock and manned by McCoy, Scott and four other crewmen, crash lands on Taurus II, a planet inhabited by hostile giants. Unable to communicate with the Enterprise or escape the planets gravitational pull, Spock devises a plan that is part logic, part human instinct.
Episode: 017 | Aired: January 12, 1967
Kirk and the Enterprise crew are alternatively entertained and tormented by Trelane, a playful being with tremendous psionic powers but little self-control.
Episode: 018 | Aired: January 19, 1967
A powerful race of beings called the Metrons transport Kirk and the lizard-like Gorn, captain of an alien ship, to an uninhabited asteroid where they are expected to resolve their differences by fighting to the death. The Metrons promise that the victor and his ship will be set free, while the loser will be destroyed, along with his ship and crew.
Episode: 019 | Aired: January 26, 1967
Accidentally transported back in time to Earth in the 20th century, the Enterprise rescues Captain John Christopher, the pilot of a destroyed fighter plane, and beams him aboard. The crew must now devise a way to return the man to Earth without changing history.
Episode: 020 | Aired: February 02, 1967
Kirks career seems doomed when he faces court-martial for actions that resulted in the death of an Enterprise crewmember.
Episode: 021 | Aired: February 09, 1967
While investigating the disappearance of the U.S.S. Archon over 100 years before; the Enterprise finds a planet controlled by a group of lawgivers known as The Body that are controlled by the omniscient Landru. The inhabitants of the planet are peaceful and staid until the coming of the Red Hour.
Episode: 022 | Aired: February 16, 1967
Kirk's crew encounters the S.S. Botany Bay, a 20th century sleeper ship from Earth that carries several bodies in suspended animation. Among them is Khan Noonien Singh, a genetically engineered superman and one of the great leaders of Earth's Eugenics War who, once awakened, reveals the rapacious ambition, strength and intelligence that helped make him ruler of a quarter of the Earth.
Episode: 023 | Aired: February 23, 1967
For over 500 years, planet Eminiar VII has waged a bizarre computer-based war with planet Vendikar. Attacks are launched and played out mathematically, but the citizens declared casualties compliantly report to disintegration stations to be vaporized. After beaming to the surface of Emimiar VII, Kirk is informed that his ship and all the crew aboard her have been declared casualties and will be executed.
Episode: 024 | Aired: March 02, 1967
Life-preserving spores on Omicron Ceti III protect the colonists there from deadly Berthold rays, but also break down inhibitions and induce feelings of total contentment. Under the influence of the spores, Spock falls into a romance with a woman who loved him long ago.
Episode: 025 | Aired: March 09, 1967
A terrifying subterranean monster with the ability to burrow through solid rock has been destroying machinery and killing miners on Janus VI, a source for the rare mineral pergium. When the creature steals a reactor pump, Spock concludes that they are dealing with an intelligent life form. He and Kirk pursue the entity, and the Vulcans mind meld sheds light on the creatures motivation.
Episode: 026 | Aired: March 23, 1967
The Enterprise offers protection to Organia, primitive planet, from the Klingons, but the Organians refuse their help. When a Klingon force attacks the planet, the Organians reveal themselves to be shockingly powerful creatures of pure energy.
Episode: 027 | Aired: March 30, 1967
A momentary blink in the stellar system leads Kirk and his crew to Lazarus, a man who seems to alternate wildly between two identities one sane, one violent.
Episode: 028 | Aired: April 06, 1967
McCoy, suffering the effects of an accidental drug overdose, leaps through a living time machine called "The Guardian of Forever" into 1930s Earth, causing serious historical changes. Kirk and Spock pursue him and arrive in Depression-era America a few days before McCoy is to arrive. Kirk must let a woman he loves die in order to restore the course of history.
Episode: 029 | Aired: April 13, 1967
On the planet Deneva, Kirk discovers his only brother, Sam, and his family have become victims of large, amoeba-like aliens that intertwine their tentacles with the human body's nervous system, causing planet-wide insanity. When Spock is attacked by one of the creatures, he volunteers to let McCoy experiment on him to find a way to kill the creatures.