The Enterprise is pulled into a reversed universe in which everyone grows younger.
The Enterprise is carrying Commodore Robert April, the ship's first captain, and his wife Sarah to Babel for his retirement. On the way, the crew tries to save a small ship racing into a supernova, and both ships are pulled through it into a negative universe where time runs backward.
The pilot, Karla Five, takes them to her home world, Arret, where her older son Karl Four helps them look for a way home, while everyone aboard grows steadily younger. With Kirk and most of the crew reduced to children, April takes command and steers the ship back, and the transporter restores everyone's proper age. Fred Bronson wrote it under the name John Culver.