The Man Trap
When a landing party beams down to an archaeological dig for a routine evaluation, one member of the party turns up dead under mysterious circumstances.
The Enterprise provides transport for 17-year-old Charlie Evans, an adolescent who grew up alone on a deserted planet, and who holds powerful abilities that were key to his survival.
Where No Man Has Gone Before
Kirk's longtime friend and fellow officer Gary Mitchell develops astounding superhuman powers, eventually turning him against his own captain and shipmates.
The Naked Time
Members of the Enterprise crew contract a virus that has intoxicating side effects, leading some to exhibit bizarre and dangerous behavior.
The Enemy Within
A transporter malfunction creates a duplicate version of Captain Kirk ... a version who has a nasty disposition.
The Enterprise rescues galactic scoundrel Harry Mudd and his hypnotically attractive passengers from a critically damaged cargo ship.
What Are Little Girls Made Of?
Brilliant scientist Dr. Roger Korby takes Kirk and Chapel hostage, revealing his hopes to replace humanity with emotionless androids.
The Enterprise encounters a planet that is an exact duplicate of Earth, but where all children die of a terrible disease as they approach adulthood.
Dagger of the Mind
Kirk takes on an investigation into the methods of Dr. Tristan Adams, a penal colony administrator who is using unique technology to control and terrorize his patients.
The Corbomite Maneuver
In uncharted space, the Enterprise encounters a mysterious alien probe. When Kirk is forced to destroy it, he incites a conflict with powerful aliens.
The Menagerie, Part I
For unknown reasons, Spock seizes control of the Enterprise and sets a course for the forbidden planet Talos IV, which he had previously visited on a mission with former Enterprise Captain Christopher Pike.
The Menagerie, Part II
As Spock faces court martial and possible execution for forcing the Enterprise to Talos IV, the mystery surrounding Captain Pike and the Talosians is slowly revealed.
The Conscience of the King
Kirk comes face to face with a criminal from the past when he learns that a political leader responsible for putting thousands to their death may be part of an acting company for which he is providing transport.
Balance of Terror
The Romulans, virtually unheard of since Starfleet was at war with them a century ago, are detected by the Enterprise to be in violation of the neutral zone, possibly testing new military technology.
Members of the crew beam down to a world where their thoughts are magically manifested into reality.
The Galileo Seven
During a shuttle mission, Spock's first command becomes a struggle of logical decisions when the team becomes stranded on a desolate planet.
The Squire of Gothos
The Enterprise crew is forced to be the guests at a party hosted by a powerful, playful, temperamental being.
Kirk and the captain of a Gorn ship, which had recently destroyed an Earth outpost, are forced to battle to the death to save their crew from certain destruction.
Tomorrow Is Yesterday
The Enterprise is hurled back in time to the 1960s, where they become the center of a U.S. Air Force pilot's UFO investigation.
Kirk faces trial for taking improper action that led to the death of a member of his crew.
The Return of the Archons
The crew investigates a strange world where the people are locked in a collective-minded zombie-like trance, at the will of a leader named Landru.
The Enterprise discovers an Earth ship that has been adrift since the late 1900s, and learns its warlike crew is still alive, having spent 200 years in suspended animation.
A Taste of Armageddon
A landing party beams down to a planet that is locked in a simulated war with one of its neighboring worlds... a war where deaths are tallied but actual destruction is avoided in order to prevent society from crumbling into ruins.
This Side of Paradise
Having beamed down to a planet to investigate the fate of a Federation research team, members of the crew become enraptured in "paradise" when they come in contact with happiness-inducing plant spores.
The Devil in the Dark
A mining colony urgently requests Kirk and his crew to stop a deadly monster that has been running rampant through the mines and killing men.
Errand of Mercy
With imminent war between the Federation and the Klingons approaching, Kirk attempts to negotiate a protection agreement with a planet caught in the middle of the dispute.
The Alternative Factor
Investigating a strange spatial phenomenon, a landing party discovers Lazarus alone on a planet, and learns of a dual inner-torment apparently at war within himself.
The City on the Edge of Forever
The crew makes the awesome discovery of a time portal, but a demented McCoy--suffering from an inadvertent medication overdose--jumps into Earth's past and radically alters history for the worse. Kirk and Spock follow McCoy through the portal to undo the damage.
Alien life seizes control of a Federation colony and its inhabitants, leaving the Enterprise as the possible last defense from a species of parasitic invaders.