Doctor Leonard “Bones” McCoy meets a former girlfriend when the enterprise brings supplies to a remote archaeological survey group. Still attractive to McCoy, the woman's current appearance hides a dark and deadly secret.
Raised from boyhood by non-corporeal beings, 17 year old Charles Evans is picked up and transferred to the Enterprise. On board the ship, the teenager proves dangerously unable to wield his enormous psionic powers with maturity.
When Enterprise encounters a Force Field at the edge of the Galaxy, one of the crew members psionic abilities are accelerated to God like proportions causing him to become a powerful murderous being.
An alien virus strips the enterprise crew of their inhibitions, causing chaos as each crew member is overcome by hidden emotions. Meanwhile, the Enterprise is being pulled inexorably into a nearby planet's gravity well.
Split by a transporter malfunction into two beings with very different personalities, the resulting twin Captain Kirk proves that neither a purely evil nor a sweetly good captain can survive without the missing half.
Rescuing the crew of a ship from an asteroid belt, the Enterprise plays host to conman extraordinaire, the cunning Harry Mudd and his cargo: three beautiful women looking for suitors.
Helping nurse Christine Chapel search for her fiancé the enterprise finds a detached Dr. Kirby working on a plan to create Android duplicates of key figures, beginning with James Kirk.
On a planet populated by children whose aging process has been slowed artificially. Kirk’s landing party members contract a virus that kills adults. Despite their violent attacks, Kirk is determined to help the children.
When a wild eyed maniac escaping from the Tantalus Penal Colony turns out to be one of the psychiatric staff, Kirk investigates the institution and discovers a chilling exercise in mind control.
Threatened by the sinister captain of a powerful alien vessel, Kirk claims that the Enterprise carries a powerful explosive which will destroy both ships. The move produces unexpected actions from the alien adversary.
Apparently summoned to Star Base 11, Kirk, Spock and McCoy visit a former Enterprise Commander, the paralyzed and horribly disfigured Christopher Pike. Uncharacteristically, Spock commandeers the Enterprise, then turns himself in for court martial.
Spock's court martial reveals the actions of Captain Pike on his previous visit to Talos IV, where the powerful Talosians tried to persuade Pike to breed with women provided for the purpose.
Contacted by one of the other two witnesses to the crimes of mass murderer “Kodos the Executioner,” Kirk is persuaded that the criminal may be disguising himself as an actor in a traveling theatrical troupe.
Despite the earlier Romulan war, the Romulans have never been seen in person. The Enterprise, in pursuit of a Romulan aggressor, makes a discovery that causes suspicion about a senior crew member.
When McCoy sees the White Rabbit from Alice in Wonderland, the crew begins to realize that the planet they are visiting seems to have the dangerous power to turn any thought into reality.
Crash landing on a planet populated by hostile giants, the 7-man crew of the shuttlecraft Galileo find themselves unable to communicate with the enterprise or to escape the planet's atmosphere.
Encountering an uncharted planet in an empty region of space, Kirk and his crew are entertained by Trelane, a playful being who lacks the self-control to wield his great psionic powers with discipline.
With both their ships held captive by powerful beings, Kirk and the captain of the alien vessel are placed on an asteroid to fight for their lives and the lives of their crews.
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.
The Federation and the Klingon Empire teeter on the brink of war as Kirk investigates Organia, a humble planet, inhabited by pacifists, that is unwittingly caught in the middle.