The Enterprise tries to save an unidentified ship plunging into a supernova but is dragged into a universe where time runs backwards. Their only hope to return home is Commodore Robert April, the first commander of the Enterprise, who is onboard on a retirement trip.moreless
The Enterprise crew encounters an alien who visited Earth in ancient times and became known as the Mayan god Kukulkan.
After passing through an unusual energy field, the Enterprise computer develops a playful--and potentially lethal--personality.
While searching for a lost ship, Kirk, Spock, and McCoy are captured and placed in a zoo by advanced, telepathic aliens.
The Enterprise goes to the center of the galaxy, where they find a race of powerful aliens who once fled Earth.