On their way to Beta Aurigae, the U.S.S. Enterprise receives a call for help from Camus II. The landing party finds only Dr. Janice Lester and Dr. Coleman, who claim that the everyone else was killed by celebium radiation. Dr. Lester was once involved with Kirk, but now harbors a deep hatred of him, because she has never been able to captain a starship in the male-dominated Starfleet. Janice traps Kirk in a mind-transfer device with her, his personality moved into her body, while she takes over his, finally becoming captain of a starship. Kirk, trapped in Janice's body, is taken to sickbay, while Janice takes control of the ship.

James Doohan (Lt. Cmdr. Montgomery Scott)
Sandra Smith (Dr. Janice Lester)
Harry Landers (Dr. Arthur Coleman)
George Takei (Lt. Hikaru Sulu)
Walter Koenig (Ensign Pavel Chekov)
Majel Barrett (Nurse Christine Chapel)
Barbara Baldavin (Communications Officer)
David L. Ross (Lt. Galloway)
John Boyer (Guard)

• NBC cancelled Star Trek, making this the series finale.
  
• This episode was originally to air in March 1969, but was pre-empted due to the death of President Eisenhower.
  
• Not allowing women to captain starships seems very un-Starfleet.
  
• Christine Chapel appears as a brunette in this episode. Majel Barrett also played Number One in the unaired pilot, who was also a brunette.
  
• Lt. Uhura was the only recurring member of the senior staff to not appear in the final episode.