Episode: 056 | Aired: September 20, 1968
When a beautiful alien surgically removes Spock's brain, the Enterprise pursues her to the sixth planet in the Sigma Draconis system, a frozen world of divided cultures, governed by an ancient and highly advanced technology.
Episode: 057 | Aired: September 27, 1968
An uncharacteristically tense and erratic Kirk takes the Enterprise into the Romulan Neutral Zone, where it is surrounded immediately. Beamed to a Roumulan ship, Kirk lies about the intrusion and then comes to blows with Spock.
Episode: 058 | Aired: October 04, 1968
When an alien device strikes Kirk with amnesia, he is stranded on a peaceful planet inhabited by descendants of Native Americans from Earth. As the captain becomes the tribes medicine man and marrying the priestess Miramanee, the Enterprise searches for a way to save the planet from collision with an asteroid.
Episode: 059 | Aired: October 11, 1968
All of the adults in the Starnes Expedition to Triacus have committed suicide, but their children appear happy and unconcerned. Kirk and the crew investigate and discover that an evil alien force, masquerading as a "friendly angel" called Gorgan, is using the children for its own nefarious purposes.
Episode: 060 | Aired: October 18, 1968
The Enterprise hosts Medusan ambassador Kollos, instrument specialist Laurence Marvick and telepath Dr. Miranda Jones. The Medusans minds are believed to be among the most beautiful in the universe, but their physical appearance is so hideously ugly. When Marvick is driven mad by a glimpse of the Medusan, he takes over the Enterprise and strands the ship in an indeterminate region beyond the edge of the galaxy.
Episode: 061 | Aired: October 25, 1968
After trespassing into Melkotian space, Kirk, Spock, McCoy, Scotty, and Chekov find themselves in an alien-created recreation of the shoot-out that took place at the OK coral in Tombstone, Arizona on October 26, 1881.
Episode: 062 | Aired: November 01, 1968
The crew of the Enterprise and a group of angry Klingons are pitted against one another by a malevolent alien creature that feeds on hatred.
Episode: 063 | Aired: November 08, 1968
Dr. McCoy is stricken with a fatal disease at the same time the Enterprise encounters an artificially propelled asteroid "vessel" that is on a crash course with a Federation planet. Kirk and Spock search for controls to redirect the ship, while McCoy falls in love with the priestess who rules the population of the asteroid.
Episode: 064 | Aired: November 15, 1968
Captain Kirk is lost and presumed dead as the Enterprise is investigating a starship that is dissolving. While waiting for interphase an opportunity to retrieve the captain Spock tries to keep the ship from being the victim of a web-like Tholian weapon and McCoy and his staff work to find the cure to a mysterious illness that threatens to drive the crew insane.
Episode: 065 | Aired: November 22, 1968
Members of the Enterprise crew are held captive on the planet Platonius by powerful telekinetics and forced to participate in a series of "games" designed to humiliate them.
Episode: 066 | Aired: November 29, 1968
The Scalosians, an alien species that exists in a hyper-accelerated time frame, commandeer the Enterprise and accelerate Kirk into their state of existence.
Episode: 067 | Aired: December 06, 1968
Trapped on the second planet of the star Minara by a radiation storm, Kirk, Spock and McCoy are captured by Vians and tortured in order to test an empathic healer's capacity for compassion and self-sacrifice.
Episode: 068 | Aired: December 20, 1968
The Enterprise ferries Elaan, the stunning Dohlman of Elas, to an arranged marriage with the leader of planet Troyius. The match would bring peace to the warring planets Elas and Troyius, but a Klingon attack threatens to disrupt the treaty between the two worlds.
Episode: 069 | Aired: January 03, 1969
Kirk and Spock are held captive in the subterranean prison for the criminally insane on Elba II by a former Starfleet hero named Garth of Izar.
Episode: 070 | Aired: January 10, 1969
Lokai and Bele, two alien men from the planet Cheron, are unable to transcend the racial bigotry that destroyed their planet. Kirk tries to mediate the conflict, but grows tired of their prejudice and decides to ignore them -- until one of them attempts to seize control of the ship.
Episode: 071 | Aired: January 17, 1969
Kirk is held captive on an exact duplicate of the Enterprise by inhabitants of Gideon -- a totally disease-free world where no one ever seems to die -- who hope he possesses the solution to their planets overpopulation.
Episode: 072 | Aired: January 24, 1969
Kirk, McCoy, Sulu and geologist D'Amato are stranded on an unexplored Class-M planet and must defend themselves against Losira, a woman who can kill people by touching them.
Episode: 073 | Aired: January 31, 1969
The Enterprise is transporting Lieutenant Mira Romaine to Memory Alpha, the central library for the United Federation of Planets, when the planetoid is attacked by a strange energy storm that kills all the inhabitants and wipes its computer memory banks clean, and then targets the Enterprise and its crew.
Episode: 074 | Aired: February 14, 1969
The crew of the Enterprise is infected with Rigellian fever, an extremely deadly plague. Kirk, Spock and McCoy beam down to Holberg 917-G in search of the only known antidote. They encounter a human man, Flint, and his daughter, Rayna. Flint becomes increasingly preoccupied with the romance blossoming between Kirk and Rayna, while the discoveries of new classical masterpieces lead to a surprising revelation.
Episode: 075 | Aired: February 21, 1969
The Enterprise is taken over by a group of rebels who are searching for the mythological Eden, reputed to be a paradise. When Spock is able to locate the planet, its promise turns out to be poison.
Episode: 076 | Aired: February 28, 1969
The Enterprise travels to the planet Ardana to obtain zienite, a rare mineral needed to cure a planet-wide plague. Zienite is mined by Troglytes, who are considered inferior beings and serve a ruling class that lives in the cloud-city of Stratos. Kirk takes action to upset the segregated, prejudicial society when McCoy discovers that Troglytes and Stratos dwellers are the same beings, but the Troglytes are adversely affected by a gas emitted during the mining of zienite.
Episode: 077 | Aired: March 07, 1969
On the planet Excalbia, Kirk and Spock are teamed with historical figures Abraham Lincoln and Surak of Vulcan. They are made to fight against Genghis Khan, Colonel Green, Zora -- a vicious killer, and Kahless, father of the Klingon Empire. The architect of the battle is a rock-like creature named Yarnek that wants to teach the Excalbians about the concepts of good and evil.
Episode: 078 | Aired: March 14, 1969
Kirk, Spock, and McCoy beam to the surface of planet Sarpeidon, intending to rescue the inhabitants before their sun goes nova. They discover the planet deserted except for a lone inhabitant, Mr. Atoz, the librarian, who has been transferring people into different periods of the planet's past. Kirk is transported to a period fraught with superstitions and witchcraft.
Episode: 079 | Aired: June 03, 1969
Dr. Janice Lester, a former lover of Kirks, harbors deep jealousy and resentment of him because she has never been able to command a starship. She secretly performs a life-entity transfer and exchanges bodies with him, trapping Kirk in her radiation-stricken body while she takes over his, finally becoming captain of a starship.