It's The (Other) Enterprise! How Discovery's I.S.S. Enterprise Connects Three Eras of Star Trek

In the classic 1967 episode, "Mirror, Mirror," when Kirk, Bones, Scotty, and Uhura accidentally beamed across dimensions, and onto another version of the Enterprise, the first clue that this was a parallel universe was the fact that the ship was orbiting around the Halkan homeworld from right-to-left, rather than left-to-right. So, the first glimpse of the I.S.S. Enterprise was simply that it was taking a different path, literally, zagging when it should have been zigging.

Ever since the debut of "Mirror, Mirror," the idea of an evil Enterprise grew in our imaginations, even if we didn't get to actually see it on-screen again. Even as the Mirror Universe expanded in Star Trek: Deep Space Nine, Star Trek: Enterprise, and Star Trek: Discovery, an on-screen glimpse of the I.S.S. Enterprise — traveling on a very different path from the U.S.S. Enterprise — remained elusive. That is, until now.

In the Discovery episode "Mirrors," the final destination of this version of the Enterprise has been revealed, and in that revelation, the entire timeline of the Star Trek universe has been traversed. Unlike the classic 1701 of the Prime Universe, the I.S.S. Enterprise's journey has lasted centuries. Here's how that journey unites at least three different aspects of the larger Star Trek story.

How Discovery Brings Back the Mirror Enterprise

In "Mirrors," the fifth episode of Discovery's fifth season, Book and Burnham take a shuttlecraft into an unstable wormhole, hoping to find a trace of Moll and L'ak and the next piece of the puzzle that can lead them to the Progenitor's elusive technology. But instead, adrift and displaced by nine centuries, and an entirely different dimension, they find the I.S.S. Enterprise, a ship Burnham never actually encountered while she was in the Mirror Universe in Discovery's first season, but is nonetheless instantly familiar with.

While aboard, we learn that while this ship was part of the Terran Starfleet. At some point after the events of "Mirror, Mirror," a group of rebellious reformers commandeered this Enterprise, turning it into a ship of hope. Book finds a plaque on the ship which commemorates the ship's journey, pointing out that "The Terran High Chancellor was killed for trying to make reforms." This could reference Mirror Spock, though Burnham and Book would have no way of knowing that.

In "Mirror, Mirror," Kirk challenged Mirror Spock to be better, and try to reform the Empire which, we learned, actually did happen. But, interestingly, Burnham and Book only have one piece of the puzzle, the audience of all of the Star Trek franchise, has the rest.

The Deep Space Nine Connection

In the 1994 Deep Space Nine episode "Crossover," Kira and Bashir find themselves in the Mirror Universe after a warp bubble kerfuffle spits them out the Bajorian wormhole and into very unfamiliar territory. They’re in the Mirror Universe all right, but this is the 24th Century version of the Mirror Universe, not the 23rd Century time frame from "Mirror, Mirror." Kira comes face to face with her Mirror self, Intendant Kira, who tells her all about how Spock became the leader of the Empire, and began "preaching reforms" and "peace."

This neatly parallels what Book says in "Mirrors," but now, we learn that some Terrans who believed in peace escaped on the I.S.S. Enterprise. While the DS9 future of the Mirror Universe was bleak for Terrans, we now learn that some survived, and even made it to the Prime Universe thanks to the Enterprise. 

The Story of Another Wayward, Vintage Starship

The Constitution-class I.S.S. Enterprise's journey from the Mirror Universe of the 23rd Century to the 32nd Century is also reminiscent of another TOS Mirror Universe starship crossover. Back in Discovery's first season, the crew learns everything they need to know about the Mirror Universe thanks to information about the U.S.S. Defiant, a ship, which like the I.S.S. Enterprise, eventually moved across universes and time, as well.

In the 1968 Original Series episode "The Tholian Web," the U.S.S. Defiant vanishes, only to reappear in the 2005 Enterprise two-parter, "In a Mirror, Darkly." As Burnham puts it in "Despite Yourself," this journey is unorthodox, "Data suggests that in the future, the Defiant will encounter a phenomenon that'll bring it into this alternative universe's past." This means that not only did the Defiant cross universes, but time-traveled too, from the 23rd Century setting of The Original Series, to the 22nd Century setting of Star Trek: Enterprise. 

The I.S.S. Enterprise didn't travel from the 23rd century Mirror Universe straight to the 32nd century Prime Universe. As we learned in Discovery's third season, crossing over directly between these universes at this point in time is impossible. But, it did crossover sometime before the end of the 24th Century; one of the mysterious 24th Century scientists, Dr. Cho, was Terran. And, that detail, brings the journey of the I.S.S. Enterprise, all the way back to the story of Discovery.

Discovery's Hopeful Mirror Universe Tale

Book reads the journey of the I.S.S. Enterprise to Burnham, mentioning that this crew escaped all thanks to the help of a "Keplian slave turned rebel leader." Instantly, Book and Burnham know this can only mean "Action Saru" himself, from the Mirror Universe.

This detail ties into Season 3's two-parter, "Terra Firma," in which Georgiou re-entered the Mirror Universe in the 23rd Century, at a point in time prior to Burnham's crossover in Season 1. But, in this version of the Mirror Universe, Georgiou, like Mirror Spock, tried to affect some positive change, which had dire consequences for her. But, at the same time, in this Mirror Universe, Georgiou had also freed Saru, and we did see him leading a rebellion toward the end of the episode. As the Guardian of Forever told Georgiou in "Terra Firma, Part 2," her actions in at least one version of the Mirror Universe had a big, positive impact, "You saved a Kelpien. And you didn't have to do that. And he'll save others. A lot of them."

So, thanks to Georgiou, Mirror Spock, and Action Saru, the story of the Mirror Universe in Star Trek: Discovery's final season has become an optimistic one. Like the idealistic Terran rebels in Deep Space Nine's "Through the Looking Glass," not all stories about the darkest dimension in Star Trek have to end in despair. And thanks to crossover between dimensions, the I.S.S. Enterprise has now become a beacon of hope in not one universe, but two.