With witches, magic and frightening experiences two aliens try to explore the influence of the human subconsciousness.

Both Klingons and humans want to forge a trading alliance with the Capellans, leading to a conflict.

An omnipotent being once worshipped as a Greek god demands reverence from the crew of the Enterprise.

Spock suffers from the Vulcan blood fever and returns to Vulcan to take the mate promised to him as a child.

The crew of the Enterprise tries to stop an ancient doomsday machine destroying entire civlizations.

On Argelius a series of mysterious murders happens that were seemingly always committed by Scotty.

A dangerous, intelligent device is beamed aboard that turns out to be an altered version of an ancient Earth probe.

On a paradisic planet, the completely immature and childlike inhabitants worship the computer Vaal.

A landing party accidentally arrives at a parallel universe where the Federation is a barbaric and violent empire.

Having been infected by a virus on Gamma Hydra, Kirk, Spcok and McCoy have to deal with accelerated aging.

The crew of the Enterprise discovers that Harry Mudd has become the sovereign of a civilization of androids.

When the Enterprise and station K-7 are crawling with high-producing tribbles, a Klingon spy can be disclosed.

Kirk, Spock and McCoy are taken hostage on a planet resembling ancient Rome and are forced to fight against gladiators in an arena.

The travel of a diplomatic corps, including Spock's father, aboard the Enterprise leads to several problems and implications.

When the Klingon interfere with a pre-warp culture,   spoiling their natural development, Kirk has to restore the balance of powers.

Kirk, Uhura and Chekov are abducted, enslaved and forced to fight for survival to entertain omnipotent beings.

Kirk becomes obsessed of hunting a being tha has killed his captain and half of the crew when he was still a young officer.

When a planetary system is threatened by a giant "space amoeba", Kirk has to send one of his friends on a suicide mission.

The Enterprise discovers that the Iotians have adapted the "philosophy" of the "mobs of the Twenties" from a book accidentally left behind.

A group of Kelvans take control of the Enterprise in order to travel back to their home, the 300 years of travel away Andromeda Galaxy.

Kirk, Spock and Ann Mulhall are taken over by three immaterial aliens who are yearning for a humanoid existence.

Due to the interference of a Federation historian, a planet's society has developed a regime very similiar to the National Socialism.

When the experimental computer control of the Enterprise leads to unforeseen problems, she becomes a danger for all ships.

In search for the crew of the Exeter, Kirk discovers that her captain supports an Omegan fraction against their enemies.

Investigating on an incident in 1968, the Enterprise encounters Gary Seven who claims to want to save Earth from a catastrophe.