The Enterprise crew try to rescue colonists from deadly radiation, but instead encounter strange alien spores that seem to offer paradise.

A shuttle crew from the USS Enterprise encounters a man out of history and his mysterious alien companion.

Captain James T. Kirk becomes obsessed with destroying a deadly entity he once encountered in his youth.

Ancient alien minds are given control of Captain Kirk's and First Officer Spock's bodies.

The Enterprise crew investigates the disappearance of a ship's crew on a planet that is a modern version of the Roman Empire.

The Enterprise travels with an alien ambassador whose appearance induces madness.

Captain Kirk is caught between dimensions while the crew of the Enterprise works to retrieve him. All the while, the Tholians demand that the Enterprise leave their space.