The U.S.S. Enterprise is sent to investigate the destruction of the Malurian system and its four billion inhabitants. When it arrives at the coordinates, the starship itself is threatened by a space going, self-contained computer/probe calling itself Nomad. When Kirk identifies himself by name, Nomad mistakes him for "The Kirk," and thinks him to be his creator.

James Doohan (Lt. Cmdr. Montgomery Scott)
Nichelle Nichols (Lt. Uhura)
George Takei (Lt. Hikaru Sulu)
Majel Barrett (Nurse Christine Chapel)
Blaisdell Makee (Lt. Singh)
Barbara Gates (Astrochemist)
Meade Martin (Engineer)
Arnold Lessing (Lt. Carlisle)
Vic Perrin (Nomad's Voice)

• Nomad was created by scientist Jackson Roykirk in the early 2000's. Nomad's program was to seek out new life and report back to Earth. Spock melds with Nomad and discovers that it was damaged and it merged with an alien probe, changing its mission to erradicate imperfect biological lifeforms. (How is Spock able to mind-meld with a machine?)
  
• Kirk convinces Nomad that it is imperfect and it self-destructs (see also "The Return of the Archons").
  
• Nomad erases Uhura's memory and she must "relearn" what the probe erased. Nomad also kills Scott, but is able to "repair" him.
  
• The story for this episode will be recycled for Star Trek: The Motion Picture.