The 33rd episode of Gene Roddenberry’s science fiction series Star Trek premieres on NBC. This is the first appearance of the “Mirror universe” plotline that recurs through the Deep Space Nine, Enterprise, and Discovery spinoff series, and remains a fan favorite. Barbara Luna guest stars. 
Stardate not given: Returning to the Enterprise from an unsuccessful mission to ask the leaders of a planet for a possible mineral trade, Kirk, Uhura, Scotty and McCoy are being beamed up just as a freak accident hurls them into another reality, which still contains a USS Enterprise and a Spock and a Federation, but the other reality’s versions are cruel and inhumane – the crew the alternate Enterprise is readying for a strike against the planet Kirk just left to take their mineral resources by force. Kirk and his landing party must try to cover their inexplicable identities and try to fit in, while stopping the savage alternate Enterprise from carrying its reign of terror any further.
written by Jerome Bixby
directed by Marc Daniels
music by Fred SteinerCast: William Shatner (Captain James T. Kirk), Leonard Nimoy (Mr. Spock), DeForest Kelley (Dr. Leonard McCoy), James Doohan (Mr. Scott), George Takei (Lt. Sulu), Nichelle Nichols (Lt. Uhura), Barbara Luna (Marlena), Victor Perrin (Tharn), John Winston (Lt. Kyle), Garth Pillsbury (Wilson), Pete Kellett (Kirk’s Henchman)
Notes: The story of what becomes of the alternate Federation and the alternate Spock is told in the 1994 Deep Space Nine episode Crossover. The divergence in history which created the alternate Federation is chronicled in the Star Trek: Enterprise two-parter In A Mirror Darkly, but an alternate explanation is offered in the For Want Of A Nail episode of the fan series Starship Farragut. The Mirror Universe is explored again in the first three seasons of Star Trek: Discovery and the spinoff movie Star Trek: Section 31.
LogBook entry by Earl Green