9/8/1966. 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.
9/15/1966. Charlie X — 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.
9/22/1966. 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.
9/29/1966. The Naked Time — Members of the Enterprise crew contract a virus that has intoxicating side effects, leading some to exhibit bizarre and dangerous behavior.
10/6/1966. The Enemy Within — A transporter malfunction creates a duplicate version of Captain Kirk ... a version who dons a nasty disposition.
10/13/1966. Mudd's Women — The Enterprise rescues galactic scoundrel Harry Mudd and his hypnotically attractive passengers from a critically damaged cargo ship.
10/20/1966. 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.
10/27/1966. Miri — 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.
11/3/1966. 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.
11/10/1966. 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.
11/17/1966. 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.
11/24/1966. 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.
12/8/1966. 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.
12/13/1966. 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.
12/29/1966. Shore Leave — Members of the crew beam down to a world where their thoughts are magically manifested into reality.
1/5/1967. 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.
1/12/1967. The Squire of Gothos — The Enterprise crew is forced to be the guests at a party hosted by a powerful, playful, temperamental being.
1/19/1967. Arena — 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.
1/26/1967. 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.
2/2/1967. Court Martial — Kirk faces trial for taking improper action that led to the death of a member of his crew.
2/9/1967. 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.
2/16/1967. Space Seed — 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.
2/23/1967. 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.
3/2/1967. 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.
3/9/1967. 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.
3/23/1967. 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.
3/30/1967. 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.
4/6/1967. 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.
4/13/1967. Operation—Annihilate! — 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.
Season 2 (1967-1968)
9/16/1967. Amok Time — Spock begins to undergo Pon Farr, the Vulcan mating cycle, forcing Kirk to set the Enterprise on a course for Vulcan.
9/22/1967. Who Mourns for Adonais? — A powerful alien halts the Enterprise in its tracks and claims to be the ancient Greek god Apollo.
9/29/1967. The Changeling — Kirk becomes the last line of defense against Nomad, a mysterious Earth probe that had been altered and given a directive to destroy anything that is imperfect.
10/6/1967. Mirror, Mirror — Kirk, McCoy, Scotty, and Uhura are beamed into a parallel universe, where murder and deceit are the common ways of its barbaric Starfleet.
10/13/1967. The Apple — While scouting a peaceful-seeming world, the Enterprise landing party finds a primitive civilization that worships a computerized entity, named Vaal, as a god.
10/20/1967. The Doomsday Machine — The Enterprise finds the crippled USS Constellation, which had been severely damaged in a battle with a powerful planet-killing doomsday weapon.
10/27/1967. Catspaw — While looking for two missing officers, the landing party becomes the captives of aliens holding a great power of illusion.
11/3/1967. I, Mudd — The Enterprise is commandeered by an android, which pilots the ship to a planet of androids who are in cahoots with the mischievous Harry Mudd.
11/10/1967. Metamorphosis — Kirk, Spock, McCoy, and a Federation negotiator become stranded when their shuttle is sucked into a celestial body by a mysterious force that has also somehow revitalized Zephram Cochrane, the man who invented warp drive two centuries before.
11/17/1967. Journey to Babel — Spock's parents, Vulcan ambassador Sarek and his wife, board the Enterprise for a Federation conference. But trouble arises when one of the delegates is murdered—and Sarek becomes a suspect.
12/1/1967. Friday's Child — While trying to negotiate trade with a planet's warlike tribal society, the Enterprise landing party is taken prisoner by one of the factions, which is dealing with the Klingons.
12/8/1967. The Deadly Years — A disease that causes rapid aging infects several members of the Enterprise crew, and eventually leaves the captain senile and unable to command the ship.
12/15/1967. Obsession — Kirk becomes convinced that a deadly gaseous cloud is an intelligent being—the same that killed 200 crew members aboard the USS Farragut, on which Kirk served 11 years earlier.
12/22/1967. Wolf in the Fold — While taking some time for R&R at a port on a peaceful alien planet, Scotty becomes the suspect in a series of murdered women.
12/29/1967. The Trouble With Tribbles — While investigating a disturbance at space station K-7, the Enterprise crew comes face to face with a group of Klingons and an even larger group of small, furry creatures known as tribbles.
1/5/1968. The Gamesters of Triskelion — Kirk, Uhura, and Chekov are kidnapped to the planet Triskelion and forced to engage in arena games to the amusement of three powerful aliens who bet on the outcomes of the fights.
1/12/1968. A Piece of the Action — Hoping to undo social damage caused by a visiting starship a century before, Kirk, Spock, and McCoy beam down to a planet whose society is based on the Chicago gangsters of the 1920s.
1/19/1968. The Immunity Syndrome — The ship encounters a huge, single-celled lifeform in space, and Kirk is forced to send either Spock or McCoy on a suicide shuttle mission to investigate methods to destroy it.
2/2/1968. A Private Little War — When the Klingons arm the aggressing side of a primitive culture with firearms, Kirk takes it upon himself to arm the other side in an effort to level the playing field.
2/9/1968. Return to Tomorrow — Kirk loans the use of his body and those of two of his crew members to aliens who exist as pure energy, so they can build robot bodies to inhabit.
2/16/1968. Patterns of Force — Investigating the disappearance of a missing Starfleet officer, an Enterprise landing party beams down to a planet modeled on Nazi Germany.
2/23/1968. By Any Other Name — Aliens who have taken human form hijack the Enterprise to use as transport back to their home galaxy.
3/1/1968. The Omega Glory — Searching for the missing crew of a Federation starship, a landing party beams down to find its captain, who has broken the Prime Directive in his obsessive search for a fountain of youth.
3/8/1968. The Ultimate Computer — The Enterprise becomes the test subject for a new starship computer system, which if successful could render most of the crew obsolete.
3/15/1968. Bread and Circuses — A landing party beams down to a parallel Earth that resembles a "20th century Rome," upon which Kirk, Spock, and McCoy are taken prisoner.
3/29/1968. Assignment: Earth — Researching history in the 20th century, the Enterprise becomes entangled with a mysterious man who is attempting to alter a historic crisis.
Season 3 (1968-1969)
9/20/1968. Spock's Brain — A woman steals Spock's brain for use as a utilities regulator on her home world, leading the Enterprise crew on a mission to retrieve it.
9/27/1968. The Enterprise Incident — Kirk, behaving erratically, steers the Enterprise into the Romulan neutral zone, where he finds himself surrounded by Romulan vessels.
10/4/1968. The Paradise Syndrome — When Kirk awakens to find himself abandoned and suffering from amnesia on a simple, primitive world, he finds happiness and love with the native people, who accept him into their tribe.
10/11/1998. And the Children Shall Lead — A landing party beams down to a research colony to find the scientists dead, and their surviving children exhibiting no signs of grief.
10/18/1968. Is There In Truth No Beauty? — The Enterprise provides transport for an alien ambassador and his companion, a human telepath trained in Vulcan mind techniques.
10/25/1968. Spectre of the Gun — An alien death sentence places Kirk and his officers in a surrealistic recreation of a showdown in the Old American West.
11/1/1968. Day of the Dove — The Enterprise becomes a battle arena when Klingon prisoners aboard the Enterprise escape their confinement and an alien being incites each side into violent confrontations with the other.
11/8/1968. For the World Is Hollow and I Have Touched the Sky — Upon analyzing an asteroid on a planetary collision course, the Enterprise crew discovers the object is actually an advanced spaceship that, to its passengers, appears to be a world of its own.
11/15/1968. The Tholian Web — An investigation of the USS Defiant, found dead in space, results in Kirk being suspended in a spatial void—leaving Spock to face a confrontation with the Tholians as McCoy attempts to cure an outbreak of insanity crippling the crew.
11/22/1968. Plato's Stepchildren — When McCoy refuses to accept permanent duties among a community of people with telekinetic powers, their leader subjects members of the Enterprise crew to cruel humiliation.
11/29/1968. Wink of an Eye — Kirk is abducted to the realm of the Scalosians, who live their lives in a vastly accelerated time continuum.
12/6/1968. The Empath — Attempting to determine the whereabouts of a missing research colony, Kirk, Spock, and McCoy suddenly find themselves the pawns in a deadly alien experiment.
12/20/1968. Elaan of Troyius — A diplomatic mission places Kirk in the role of etiquette teacher for a warrior whose world needs her to make peace with its long-embittered neighbor.
1/3/1969. Whom Gods Destroy — While delivering medicine to a penal colony for the insane, Kirk and Spock are taken prisoner by a megalomaniac bent on unleashing his wrath upon the universe.
1/10/1969. Let That Be Your Last Battlefield — The Enterprise becomes the latest battleground for the millennia-spanning strife between two bitter enemies from a world paralyzed by racial hatred.
1/17/1969. The Mark of Gideon — Upon beaming down to the planet Gideon, Kirk finds himself on a duplicate of the Enterprise with a woman who yearns of a place where she can escape the extreme overpopulation of her home world.
1/24/1969. That Which Survives — A landing party must solve the mystery of a woman who is the cause of several crew members' deaths and the sabotage of the ship's engines.
1/31/1969. The Lights of Zetar — Scotty falls for a woman who becomes the latest target of a non-corporeal alien presence in need of a human form.
2/14/1969. Requiem for Methuselah — While searching for a needed medicine to combat a plague, the Enterprise landing party encounters a social recluse who had long ago abandoned Earth and now lives alone with his enigmatic pupil.
2/21/1969. The Way to Edenzero stars — A group of non-conformists takes control of the Enterprise and sets it on a course for the mythical planet of Eden.
2/28/1969. The Cloud Minders — While attempting to obtain a crucial mineral to cure a planetary plague, Kirk is drawn into the struggle of a world divided by class exploitation.
3/7/1969. The Savage Curtain — An entity claiming to be Abraham Lincoln invites Kirk and Spock to the planet surface, where an advanced lifeform vies to study the methodologies of both good and evil.
3/14/1969. All Our Yesterdays — The landing party investigates the final hours of a planet whose star is going supernova, and whose people have escaped the coming death of their world by traveling into their society's past.
6/3/1969. Turnabout Intruder — One of Kirk's former lovers, consumed with jealousy and bitterness for being denied a Starfleet captaincy, renders Kirk unconscious and trades bodies with him, assuming his identity and abusing the powers of his command.