While exploring "The Delta Triangle," where many starships have disappeared, the U.S.S. Enterprise is attacked by several Klingon vessels. During the battle, they are caught in an ion storm. The Enterprise and one Klingon battlecruiser are drawn into a spacetime vortex and end up in a timeless dimension.

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 (Nurse Christine Chapel)
James Doohan (Lt. Cmdr. Montgomery Scott)

• Commander Kor was the first Klingon shown on screen, seen in the classic episode "Errand of Mercy". In his live action appearance he was played by John Colicos, who would later reprise the role in the Deep Space 9 episode "Blood Oath". (He is naturally voiced by James Doohan here.)
  
• Kor's ship is given the name I.K.S. Klothos in this epsidoe.