The U.S.S. Enterprise is escorting Commodore Robert April and his wife Dr. Sarah April, the first captain and chief medical officer of the U.S.S. Enterprise, to Commodore April's retirement ceremonies on Babel. While en route, an alien vessel passes the U.S.S. Enterprise at warp 36 toward heading directly into the Beta Niobe nova. Locking onto the alien ship with the tractor beam, the U.S.S. Enterprise is dragged along, unable to break free; both ships fall into the nova and arrive in an antimatter universe where time flows backwards.

The alien ship's pilot, Karla Five, is an explorer from the reverse universe who accidentally became lost in our universe. He leads the U.S.S. Enterprise to his home world of Arret to help find a way back into normal space. On Arret, the crew encounter an old man, who is Karla Five's son, and a baby, his father. The crew begin to notice that they too are getting younger as they remain in the negative universe.

In time they discover a dead star that corresponds to the nova in the positive universe; it is the gateway for the U.S.S. Enterprise's return. Though Karla Five's ship is strong enough to pull the starship through the nova, the Enterprise crew is now too young to pilot it. Commodore April, now a young handsome man, takes command of the ship steering it back through the nova. Using the transporter, April restores the crew to their proper age. The Aprils consider remaining young, but instead decide that they have lived their lives to the fullest. Once back to their original ages, the Federation decides to change the mandatory retirement age and the Aprils are able to continue their careers.

Cast:

William Shatner as James T. Kirk
Leonard Nimoy as Spock
DeForest Kelley as Leonard H. McCoy
James Doohan as Montgomery Scott
Nichelle Nichols as Uhura
George Takei as Hikaru Sulu

Guest Cast:

James Doohan as Commodore Robert April
Nichelle Nichols as Dr. Sarah April
Nichelle Nichols as Karla Five
James Doohan as Karl Four
James Doohan as Lieutenant Arex

Creative Staff:

Written By: John Culver
Director: Bill Reed