In orbit around a dead star, the Enterprise comes across a huge starship inhabited by a parasitic life form that threatens the entire ship.

Spock travels back in time to prevent his death as a young Vulcan.

The crew of the Enterprise races to find a way to stop a cloud from destroying inhabited planets.

Female crew members must take over the Enterprise when the men are incapacitated by a race of sirens.

Cyrano Jones introduces tribbles that cannot reproduce.

The Enterprise finds a long-lost explorer.

A race of plant people, and their master, have a plan to force peace onto the galaxy.

At the center of the galaxy, the Enterprise discovers a race of powerful aliens.

Kirk returns to the "shore leave" planet, but it's not as peaceful as it was when they last saw it.

Space con artist Harry Mudd returns, selling a fake love potion.

The Enterprise crew begins to shrink after radiation exposure.

The Enterprise crew must work with Klingons to escape from a pocket universe.

While exploring the planet Argo, Kirk and Spock are turned into water breathers.

Spock, Sulu, and Uhura discover a time capsule from an ancient and technologically advanced race. However, it draws some unwanted attention.

Telepathic aliens put Kirk, Spock and McCoy in a zoo.

Kirk and Spock are recruited for a heist to recover a stolen relic, which if not recovered could spark an galactic jihad.

With Spock stricken down by a fatal disease, the Enterprise must track down the drug that can cure him before it is too late.

The Enterprise crew is joined by a unpredictable alien called Ari bn Bem, an independent observer from the planet Pandro.

The computer of the Enterprise gains partial sentience and starts playing practical jokes on the crew.

Dr. McCoy is arrested and held responsible for causing a plague that ravaged the planet Dramia II, where he performed a mass-innoculation 19 years earlier.

The Enterprise runs into a being that once visited Earth and influenced the Mayan culture.

With Commodore Robert April (the first commander of the Enterprise) on board, Kirk pursues a ship plunging into a supernova, and enters a universe where time runs backwards.