The third and final season of the original Star Trek aired Fridays at 10:00-11:00 pm on NBC from September 20, 1968 to March 14, 1969. The final episode aired Tuesday, June 3, 1969 at 7:30-8:30 pm.
Kirk leads the Enterprise in pursuit of a mysterious alien woman after she beams aboard the bridge and steals Spock's brain.
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.
Spock and the Enterprise crew race to destroy an asteroid threatening a primitive world where an amnesiac Kirk is proclaimed a god by its indigenous people.
The Enterprise travels to a planet where the members of a scientific team appear to have killed themselves. Their orphaned children are brought back to the ship, where they begin exhibiting odd behavior.
The Enterprise hosts an alien ambassador whose outward appearance induces madness in humanoids. When Spock is driven mad after an unfortunate oversight, only the ambassador's jealous telepathic companion can save his mind.
When coming to an exaphobic isolationist planet, Captain Kirk and his landing party are punished for trepassing. They are sentenced to death in a surreal recreation of the Gunfight at the OK Corral with the landing on the losing side.
When the Enterprise brings aboard Klingon prisoners, an alien entity pits both sides against each other in an ever-escalating struggle.
The Enterprise must deflect an asteroid on a collision course with an inhabited planet... but discover the asteroid is a spaceship with a population unaware of the outside world.
Captain Kirk finds himself trapped between dimensions on a disintegrating starship. The Enterprise crew works against time to rescue him as the Tholians weave a destructive energy web around their ship.
Kirk and his crew find themselves at the mercy of powerful individuals who possess mind-over-matter powers... and plan to use the Enterprise crew for their twisted entertainment.
Invisible to humans due to their time-accelerated state, a group of aliens invade the Enterprise and attempt to abduct members of the crew to serve as breeding stock for their dying planet.
On a planet doomed to destruction, Kirk, Spock & McCoy become involved with two aliens who use them as laboratory animals in a bizarre series of tests on an alien empath who may be the savior of her planet.
The Enterprise must escort an alien princess to her marriage to seal an interplanetary alliance... but she becomes attracted to Kirk.
Kirk and Spock investigate an insane asylum where a former Starfleet captain is being held, only to discover that he has freed the inmates and is running the place.
The Enterprise finds itself host to two alien beings from the same planet, who share an intense and self-destructive hatred of each other.
Kirk beams down on a diplomatic mission... and finds himself in an Enterprise where all the crew have vanished and only a mysterious woman resides.
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.
The Enterprise must deal with discorporeal cloud-like corporeal aliens who have already destroyed the inhabitants of a library planet and plan to eliminate the Enterprise crew if they cannot acquire a human host.
While seeking a cure for a fever ravaging the Enterprise, Kirk and Spock encounter Flint, a hermit-like Earthman, and his beautiful young ward.
The Enterprise picks up a group of space "hippies" looking for Eden.
Kirk must resolve a mining dispute on a the cloud city of Stratos to acquire the resources to cure a space plague.
Kirk and Spock meet Abraham Lincoln and Surak of Vulcan and must do battle with some of histories most terrible villians.
Kirk, Spock, and McCoy become trapped in the past of another world.