The crew of the Enterprise visits an abandoned outpost guarded by a mysterious computer.

The crew of the Enterprise encounters an immortal human who lives as a recluse on his own planet.

The Enterprise is hijacked by a criminal doctor and his loyal, hippie-like followers who are attempting to find paradise

An overpopulated race of aliens abduct Kirk to solve their problem.

The Enterprise picks up the last two survivors of a war-torn planet who are still committed to destroying each other aboard the ship.

Captain Kirk visits a mental health facility and confronts an insane starship captain who believes he is destined to control the Universe.

Captain Kirk hosts a spoiled Princess, who must bring peace to a star system at war.

While visiting a doomed planet, the landing party is subject to torturous experiments to test an empathic race.

Invisible “time-accelerated” aliens take over the Enterprise and attempt to abduct the crew for use as “genetic stock.”

Captain Kirk is caught between dimensions while the Enterprise is trapped by an energy draining web spun by mysterious aliens. The two-part Enterprise episode “In a Mirror, Darkly” serves as a sequel to this episode.

As McCoy discovers he is dying of an incurable disease, the crew of the Enterprise rush to stop an asteroid from colliding with a Federation world, only to discover that the asteroid is, in fact, a disguised alien vessel. They find an

An alien energy-based life form that feeds on negative emotions (such as fear, anger, hatred) drives the crew of the Enterprise into brutal conflict with the Klingons.