When a time vortex erases Spock from the crew's memories, he must travel to the past to rescue his younger self from danger.

William Shatner (Captain James T. Kirk)
Leonard Nimoy (Commander Spock)
DeForest Kelley (Dr. Leonard H. McCoy)

George Takei (Lt. Hikaru Sulu)
Nichelle Nichols (Lt. Uhura)
Majel Barrett (Amanda Grayson)
James Doohan (Lt. Cmdr. Montgomery Scott)
Mark Lenard (Ambassador Sarek)
Billy Simpson (Young Spock)
Keith Sutherland (Sepek)

• The Enterprise crew first encounters the Guardian of Forever in the classic episode "The City on the Edge of Forever".
  
• Upon their return, the first officer of the Enterprise is Commander Thelin, the first Andorian shown as a member of Starfleet.
  
• Spock's pet sehlat, I-Chaya, is mortally wounded.
  
• Mark Lenard returns to voice Ambassador Sarek.
  
• In addition to playing Amanda Grayson, Majel Barrett does double duty as the historian Grey.
  
• In addition to voicing Scotty, James Doohan voices Commander Thelin, the Guardian of Forever and most of the other background characters.