Air date: 1967-09-15

Runtime: 50 min

First Officer Spock returns to his home world for a brutal Vulcan mating ritual.

Air date: 1967-09-22

Runtime: 51 min

The crew of the Enterprise are held captive by an alien who turns out to be the Greek god Apollo.

Air date: 1967-09-29

Runtime: 50 min

The crew of the USS Enterprise deals with an indestructible planet-destroying space probe.

Air date: 1967-10-06

Runtime: 50 min

A transporter mishap swaps Captain Kirk and his companions with their evil counterparts in a parallel universe. In the so-called Mirror Universe, the Enterprise is a ship of the Terran Empire, an organization as evil as the United Federation of Planets is benevolent.

Air date: 1967-10-13

Runtime: 50 min

The crew of the Enterprise visits a mysterious paradisical planet controlled by a computer that is served by the local inhabitants.

Air date: 1967-10-20

Runtime: 51 min

The starship Enterprise and its heavily-damaged sister ship, the USS Constellation, must work together to stop an alien planet-killing machine headed for the heart of Federation territory.

Air date: 1967-10-27

Runtime: 50 min

Two powerful aliens threaten the well-being of the Enterprise and her crew.

Air date: 1967-11-03

Runtime: 51 min

Captain Kirk has a second run-in with the conman, Harry Mudd. Mudd is now the supreme ruler of a planet of androids who cater to his every whim.

Air date: 1967-11-10

Runtime: 50 min

A shuttle crew from the USS Enterprise encounters a man out of history and his mysterious alien companion.

Air date: 1967-11-17

Runtime: 50 min

The Enterprise must transport dignitaries to a peace conference, with an assassin on the loose.

Air date: 1967-12-01

Runtime: 50 min

The crew of the Enterprise become entangled in a planet's tribal power struggle.

Air date: 1967-12-08

Runtime: 50 min

Strange radiation exposes the command crew of the Enterprise to the effects of rapid aging.

Air date: 1967-12-15

Runtime: 50 min

Captain James T. Kirk becomes obsessed with destroying a deadly entity he once encountered in his youth.

Air date: 1967-12-22

Runtime: 51 min

A series of bizarre murders points to Mr. Scott as the prime suspect.

Air date: 1967-12-29

Runtime: 50 min

The Enterprise must protect a very important shipment of grain from both Klingons and some adorable creatures called tribbles.

Air date: 1968-01-05

Runtime: 50 min

Captain Kirk and his companions are abducted into slavery and trained to fight as gladiators for the gambling entertainment of three disembodied beings.

Air date: 1968-01-12

Runtime: 50 min

The Enterprise visits a planet with an Earth-like 1920s gangster culture.

Air date: 1968-01-19

Runtime: 50 min

The crew of the Enterprise encounters an energy-draining field which may be able to destroy the galaxy.

Air date: 1968-02-02

Runtime: 51 min

The crew of the Enterprise discovers Klingon interference in the development of a formerly peaceful planet and is forced to help maintain a balance of power.

Air date: 1968-02-09

Runtime: 50 min

Ancient alien minds are given control of Captain Kirk's and First Officer Spock's bodies.

Air date: 1968-02-16

Runtime: 50 min

The crew of the Enterprise tracks down a Federation observer on a planet dominated by a "Naziesque" regime.

Air date: 1968-02-23

Runtime: 50 min

Beings from another galaxy commandeer the Enterprise in an attempt to return home.

Air date: 1968-03-01

Runtime: 50 min

Captain Kirk must find the cure to a deadly disease and put an end to another Starfleet captain's cultural interference.

Air date: 1968-03-08

Runtime: 50 min

A skeleton Enterprise crew are assigned to test a revolutionary computer system that is given total control of the ship.

Air date: 1968-03-15

Runtime: 50 min

The Enterprise crew investigates the disappearance of a ship's crew on a planet that is a modern version of the Roman Empire.

Air date: 1968-03-29

Runtime: 50 min

While back in time observing Earth in 1968, the Enterprise crew encounters the mysterious Gary Seven who has his own agenda on the planet.