Air date: 1968-09-20

Runtime: 51 min

An alien female beams aboard the ship and, after incapacitating the rest of the crew, surgically removes Spock's brain. Kirk and the crew have just hours to locate and replace it before Spock's body dies.

Air date: 1968-09-27

Runtime: 51 min

The crew of the Enterprise are on a secret mission to steal a Romulan cloaking device.

Air date: 1968-10-04

Runtime: 51 min

An alien device on a primitive planet erases Captain Kirk's memory, and he begins a new life with the planet's indigenous people.

Air date: 1968-10-11

Runtime: 51 min

On a distant planet, Kirk, Spock and McCoy find a scientific team dead, and their children who, unknown to the crew, have great powers at their disposal.

Air date: 1968-10-18

Runtime: 51 min

The Enterprise travels with an alien ambassador whose appearance induces madness.

Air date: 1968-10-25

Runtime: 51 min

Having been found trespassers into Melkotian space, Captain Kirk and his companions are sent to die in a re-enactment of the gunfight at the O.K. Corral.

Air date: 1968-11-01

Runtime: 51 min

An alien force drives the crew of the Enterprise into brutal conflict with the Klingons.

Air date: 1968-11-08

Runtime: 51 min

The crew of the Enterprise rush to stop an asteroid from colliding with a Federation world, but discover the asteroid is actually an inhabited generation ship.

Air date: 1968-11-15

Runtime: 50 min

Captain Kirk is caught between dimensions while the crew of the Enterprise works to retrieve him. All the while, the Tholians demand that the Enterprise leave their space.

Air date: 1968-11-22

Runtime: 51 min

The crew of the Enterprise encounters an ageless and sadistic race of humanoids with the power of telekinesis and who claim to have organized their society around Ancient Greek ideals.

Air date: 1968-11-29

Runtime: 51 min

Invisible "time-accelerated" aliens take over the Enterprise and attempt to abduct the crew for use as "genetic stock".

Air date: 1968-12-06

Runtime: 51 min

While visiting a doomed planet, the landing party is subject to torturous experiments by powerful aliens.

Air date: 1968-12-20

Runtime: 51 min

The USS Enterprise ferries a spoiled princess whose betrothal to a royal Troyian is hoped will bring peace to a star system at war.

Air date: 1969-01-03

Runtime: 51 min

Captain Kirk faces off with a demented shape-shifting starship captain determined to control the universe.

Air date: 1969-01-10

Runtime: 51 min

The Enterprise encounters two duo-chromatic and mutually belligerent aliens who put the ship in the middle of their old conflict.

Air date: 1969-01-17

Runtime: 51 min

A race of overpopulated aliens abduct Captain Kirk to solve their problem.

Air date: 1969-01-24

Runtime: 51 min

Kirk, McCoy, and Sulu are stranded on a barren planet where a mysterious woman attempts to kill them one at a time, while the Enterprise must travel halfway across the galaxy to rescue them.

Air date: 1969-01-31

Runtime: 51 min

Strange incorporeal aliens threaten the Memory Alpha station and the Enterprise.

Air date: 1969-02-14

Runtime: 51 min

The crew of the Enterprise encounter an immortal human in this science fiction variation on Shakespeare's The Tempest.

Air date: 1969-02-21

Runtime: 51 min

The Enterprise picks up a group of space "hippies" looking for Eden.

Air date: 1969-02-28

Runtime: 51 min

Captain Kirk races against time to acquire plague-fighting minerals from a world in the midst of a civil uprising against a grievous social class disparity.

Air date: 1969-03-07

Runtime: 51 min

Aliens force Captain Kirk and First Officer Spock to join forces with "Abraham Lincoln" and "Surak" to battle villains in a contest of good vs. evil.

Air date: 1969-03-14

Runtime: 51 min

Kirk, Spock and McCoy are trapped in two parts of another planet's past - a world threatened with destruction when its sun goes supernova.

Air date: 1969-06-03

Runtime: 51 min

The Enterprise is in danger when Janice Lester, one of Kirk's former lovers, steals his body.