#1 - The Trouble With Tribbles 8.48
Season 2 - Episode 15
Kirk must defuse a Klingon scheme to destroy a grain shipment...and cope with a seemingly benign creature known as a tribble, which reproduces at amazing speed.
#2 - The City on the Edge of Forever 8.47
Season 1 - Episode 28
Kirk and Spock must travel into the past in order to correct a change that will alter history.
#3 - Balance of Terror 8.36
Season 1 - Episode 14
Kirk pits the Enterprise against an invisible spaceship testing the Federation's defenses.
#4 - Space Seed 8.31
Season 1 - Episode 22
The Enterprise picks up a crew of genetic supermen from the 20th century...and their leader, Khan, plans to create a new empire.
#5 - Amok Time 8.19
Season 2 - Episode 1
Spock must go to Vulcan in order to perform the Vulcan mating ritual.
#6 - Mirror, Mirror 8.17
Season 2 - Episode 4
Kirk and three of his officers are accidentally transported into a parallel ""mirror"" universe where violence, greed, and evil are commonplace.
#7 - Journey to Babel 8.13
Season 2 - Episode 10
Spock meets his estranged father when the Enterprise escorts a group of ambassadors to a conference on the planet Babel.
#8 - The Enterprise Incident 8.08
Season 3 - Episode 2
An unusually tense and irritable Kirk orders his ship into the Romulan Neutral Zone, where it is promptly surrounded. Beamed to a Romulan ship, Kirk lies about the intrusion, then attacks Spock, who responds with a Vulcan death grip. While the female Romulan commander courts Spock, a secret mission unfolds.
#9 - The Ultimate Computer 8.01
Season 2 - Episode 24
The Enterprise is used to test a new super-sophisticated computer, but it soon develops a mind of its own.
#10 - The Doomsday Machine 8.01
Season 2 - Episode 6
The Enterprise must stop an ancient doomsday weapon that is capable of destroying entire worlds...and has already totalled one Constellation-class cruiser.
#11 - A Taste of Armageddon 7.93
Season 1 - Episode 23
The Enterprise arrives at a planet to establish diplomatic relations and finds itself in the middle of a "peaceful" war that threatens to destroy the ship.
#12 - The Tholian Web 7.93
Season 3 - Episode 9
Stardate 5693.2: The Enterprise arrives at the last known position of the U.S.S. Defiant (NCC-1764), an area of uncharted space, to search for the missing starship. When the Defiant appears on the viewing screen enshrouded in a strange green glow, Spock is unable to scan the vessel on his sensors. Kirk beams over to the Defiant with a boarding party to investigate and finds the entire crew dead. What's more, the Defiant seems to be trapped in an interphase between two different universes. A power loss partially disables the Enterprise transporter, but the landing party manages to beam back to the Enterprise except Kirk who suddenly disappears along with the Defiant. Spock calculates that the next time to interphase will be approximately two hours, and that the captain can be rescued at that time. As the Enterprise begins to experience the same problems that doomed the Defiant: power loss, weakness and insanity among the crew, an alien vessel appears and demands that they leave Tholian
#13 - The Menagerie (1) 7.91
Season 1 - Episode 11
Spock kidnaps his former captain, the crippled Christopher Pike, and heads for a quarantined planet, putting his career and Kirk's life on the line.
#14 - Tomorrow is Yesterday 7.90
Season 1 - Episode 19
The Enterprise collides with a black hole and is thrown back to Earth in the 20th century, where they must find a way back and erase any trace of their presence. Matters become complicated when they rescue an Air Force pilot and cannot return him without changing history...but if he disappears that will change history as well.
#15 - Assignment: Earth 7.86
Season 2 - Episode 26
Stardate not given: The Enterprise is sent on a mission back to Earth in the year 1968 to discover details about how the planet survived the arms race. While in orbit, the ship intercepts a transporter beam from an unknown part of the galaxy and beams the space traveler aboard. Surprised by what has taken place, the man identifies himself as Gary Seven and claims to be a 20th Century Earthman raised on an unknown world and trained to prevent Earth from destroying itself. Kirk decides to verify Seven's story before releasing him, but Seven escapes and beams down to the planet below. Kirk and Spock follow him to New York City, and Seven meanwhile discovers that two of his fellow agents have been killed in a auto accident. Seven is forced to complete their mission himself which is to sabotage an orbital nuclear platform, just low enough in the atmosphere to scare Earth leaders into prohibiting additional nuclear space weapons. Just as Kirk and Spock arrive, Seven beams out of his office a
#16 - Court Martial 7.85
Season 1 - Episode 20
Captain Kirk's career is at stake when he is put on trial for the loss of a crewman during an ion storm.
#17 - The Devil in the Dark 7.73
Season 1 - Episode 25
Kirk investigates a series of grisly murders on a mining planet that are the work of a seemingly hostile alien creature.
#18 - Errand of Mercy 7.72
Season 1 - Episode 26
The Federation and the Klingon Empire teeter on the brink of war as Kirk investigates a humble planet caught in the middle - Organia, inhabited by pacifists
#19 - All Our Yesterdays 7.72
Season 3 - Episode 23
Kirk, Spock, and McCoy become trapped in the past of another world.
#20 - Patterns of Force 7.72
Season 2 - Episode 21
The Enterprise seek out a historical researcher and discover he has contaminated a culture, rendering it into a near-duplicate of Nazi Germany.
#21 - Wink of an Eye 7.71
Season 3 - Episode 11
Stardate 5710.5: When a landing party investigating Scalos begins to vanish one by one, Kirk, Spock and McCoy try to find out what is happening before more of the crew disappears, until Kirk himself is abducted. Kirk finds the cause to be a group of endangered Scalosians who move faster than human sight or hearing can detect. They need to repopulate their species, and find that speeding human males up to Scalosian speed will meet their needs. Kirk must find a way to get a message to Spock and McCoy, who are working on a cure for the mystery ""ailment,"" as well as stirring up fighting among the Scalosians, before they have control of the Enterprise.
#22 - The Changeling 7.70
Season 2 - Episode 3
The Enterprise encounters an ancient Earth probe bent on the sterilization of all life.
#23 - This Side of Paradise 7.67
Season 1 - Episode 24
The Enterprise crew is trapped in paradise when they come to rescue colonists who have fallen to pacifying alien spores and become infected themselves.
#24 - The Menagerie (2) 7.66
Season 1 - Episode 12
Spock's court-martial continues as he attempts to justify his abduction of Pike, the theft of the Enterprise, and his heading for a planet declared forbidden by Starfleet.
#25 - The Naked Time 7.66
Season 1 - Episode 4
A strange alien substance causes the crew to act out their deepest inhibitions, while the ship plummets out of orbit.