Star Trek's Mirror Universe is one of the most mysterious alternate universes in the show's lore, as it is everything that is the exact opposite of the Prime Universe. The Mirror Universe was first introduced in the 1960s in season 2 of The Original Series, and has since been expanded upon with almost every new iteration of Star Trek.
In the Mirror Universe, which is (most of the time) ruled by the totalitarian Terran Empire, characters will often encounter their evil doppelgangers, which has resulted in interesting stories and episodes. There are a few Mirror Universe episodes that have had a lasting impact on Star Trek and fans, which still hold up today as some of the best episodes in the franchise.
7 Mirror, Mirror
IMDb Score: 9/10
- Star Trek: The Original Series
- Season 2, episode 4
The first episode ever to explore the Mirror Universe in Star Trek was the Original Series episode "Mirror, Mirror." Out of all the Mirror Universe episodes to date, "Mirror, Mirror" also still holds the highest rating of all, perhaps because it is iconic in the sense that it introduces the Mirror Universe to Star Trek canon.
In this episode, due to a transporter accident involving an ion storm (as usual), some members of the USS Enterprise crew find themselves in an alternate universe. Here, side arms are standard issue, Spock has a goatee, and their ship is called the ISS Enterprise. By the end of the episode, Kirk, McCoy, Uhura, and Scott return to the Prime Universe, but the door has been opened for many more Mirror Universe episodes in Star Trek's future.
6 The Tholian Web
IMDb Score: 8/10
- Star Trek: The Original Series
- Season 3, episode 9
The only other Mirror Universe episode in The Original Series is "The Tholian Web." This episode is action-packed, introducing a new species called the Tholians; a ship that becomes iconic to the Mirror Universe, the Defiant; and featuring one of those times that audiences thought Kirk died. This episode is considered one of the best Spock episodes from The Original Series, and one of the best Star Trek episodes ever to air.
In search of the USS Defiant, the Enterprise enters an uncharted region of space where the Defiant is found adrift, phasing in and out of the known universe. The Tholians arrive, weaving an energy web around the Enterprise, while Kirk's "ghost" appears on the Enterprise. After a miraculous turn of events (as usual), Kirk is returned to the Prime Universe unharmed, and they are on their way.
5 Crossover
IMDb Score: 7.9/10
- Star Trek: Deep Space Nine
- Season 2, episode 23
Star Trek: Deep Space Nine is one of the Star Trek series that features the most Mirror Universe episodes, having five episodes from five seasons dedicated to the Mirror Universe. Not all the Mirror Universe episodes from Deep Space Nine were successful though. Only one stands out, the must-see Star Trek episode for any fan: "Crossover." Unlike many other Mirror Universe episodes, "Crossover" makes reference to the first-ever Mirror Universe episode from The Original Series.
In this era of the Mirror Universe, the Terrans are slaves and Deep Space Nine is a mining station, run by Kira Nerys' evil counterpart, the Intendant. After much scheming and back-stabbing, Kira and Bashir, who stumbled upon the Mirror Universe through a wormhole, manage to return to the Prime Universe unharmed.
4 In A Mirror, Darkly
IMDb Score: 8.3/10
- Star Trek: Enterprise
- Season 4, episodes 18 and 19
The two-parter episode "In a Mirror, Darkly" is an epic Mirror Universe episode filled with Easter eggs from "The Tholian Web" and from the movie, Star Trek: First Contact. This episode is unique, as it does not feature characters from the Prime Universe that travel to the Mirror Universe. Rather, it follows events in the Mirror Universe that involve the Mirror versions of the Enterprise crew.
The episode starts off with First Contact between the humans and the Vulcans, but instead of the peaceful encounter that takes place in First Contact, Zefram Cochrane shoots the Vulcan ambassador. This is when viewers realize that this is an alternate universe. The two episodes are action-packed, ending with the crowning of Empress Sato after she poisons Mirror Archer.
3 Vaulting Ambition
IMDb Score: 8.1/10
- Star Trek: Discovery
- Season 1, episode 12
Star Trek: Discovery is the Star Trek series that features the most Mirror Universe episodes to date. In nine episodes over four seasons, characters from the Prime Universe find themselves in the Mirror Universe. On top of this, two Mirror characters remain in the Prime Universe for extended periods of time: Gabriel Lorca and Emperor Philippa Georgiou.
"Vaulting Ambition" is filled with plot twists, mainly the big reveal that Gabriel Lorca, whom Michael Burnham (the show's main protagonist) thought was Captain Lorca of the USS Buran, is actually Mirror Lorca. Paul Stamets also meets his evil counterpart, and they navigate the visually stunning mycelial network in an attempt to rectify the damage that Mirror Stamets has done.
2 What's Past is Prologue
IMDb Score: 8.1/10
- Star Trek: Discovery
- Season 1, episode 13
With its serial format optimized for streaming platforms, on which Discovery first aired, the show manages to keep the suspense from "Vaulting Ambition" as it goes into the next episode, "What's Past is Prologue." As Lorca escapes from the agonizer (a nice throwback to "Mirror, Mirror"), he and his loyalists attempt to overthrow Emperor Georgiou as ruler of the Terran Empire.
The episode is filled with gun fights, masterful fighting sequences performed by Oscar-winning Michelle Yeoh, and another huge twist. Just as Emperor Georgiou gets ready to sacrifice herself so that Michael Burnham can beam back to the Prime Universe, Burnham grabs onto her and the two beam back together. This action puts in motion many significant events that revolve around Emperor Georgiou in the Prime Universe in episodes to follow.
1 Terra Firma
IMDb Score: 6.4/10
- Star Trek: Discovery
- Season 3, episodes 9 and 10
While the two-parter Terra Firma has received one of the lower IMDb scores of the Mirror Universe episodes, it is worth consideration as one of the best Star Trek Mirror Universe episodes. In "Terra Firma," a dying Emperor Georgiou is sent back to the Mirror Universe by the Guardian of Forever - an omniscient being introduced in a classic Original Series episode many decades ago, "The City on the Edge of Forever." "Terra Firma" is therefore filled with Easter eggs for die-hard Star Trek fans.
While it might seem controversial for some, it gives one of the most evil characters in the Prime and Mirror Universe a chance at redemption. Showing that humanity can change for the better is a theme at the core of Star Trek, and "Terra Firma" does a great job at doing that.
Star Trek
Star Trek is a space exploration franchise originally created by Gene Roddenberry. The series has spanned shows like The Original Series, The Next Generation, and Voyager. More recently, developer Scopely came out with Star Trek Fleet Command, a mobile title where you get to be captain of your own ship.
