WARNING: The following article contains spoilers for the midseason premiere of Star Trek: Discovery, “Despite Yourself,” which debuted Sunday on CBS All Access.
The last time Star Trek fans visited the Mirror Universe was roughly 15 years ago, in a two-part episode of Enterprise. The memorable "In a Mirror Darkly" represents the only time the franchise has set a story solely in the Mirror Universe without any action or characters set in the Prime Universe. Well, almost.
The story centers around the Mirror counterparts of the Prime Enterprise crew, with obvious adjustments. Archer is the first officer of the I.S.S. Enterprise, and he's pretty pouty about it. But he hasn't murdered his captain, yet, so his career is going nowhere. Then the crew comes across a Constitution-class ship from the Prime Universe (the U.S.S. Defiant), but a century into the future. TL;DR - it's chock-full of deliciously exploitable tech.
And exploit the tech, they do. Archer uses the ship to crush the rebellion the Empire is fighting and then declares himself Emperor because, why not? The canon's a little wonky on how, after a century, the Mirror Universe hasn't evolved beyond the technology appropriated 100 years earlier before (in the Original Series episode "Mirror, Mirror," tech hasn't moved beyond what we see on Defiant), but considering the Empire is less concerned with exploration and bettering itself than it is with subjugating everyone else, it kind of makes sense.
The important thing is that these episodes establish is a precedent for someone from the Mirror Universe poaching technology from the Prime Universe and using it to their advantage. On Sunday's episode of Star Trek: Discovery, we learned there are records of the Defiant's arrival a century before, and if someone in the present Mirror Universe were to get their hands on, say, a spore drive? Well, that person might be able stage their own coup just like Archer tried to. But who would do such a thing?
As Starfleet captains go, Gabriel Lorca (Jason Isaacs) is ... unique. He's harsh, demanding, manipulative and decidedly uninterested in following Starfleet protocol unless it suits him. Those qualities aren't exactly damning when you take into context the fact that Lorca is a wartime captain, not to mention Discovery's deliberate tonal departure from the rest of the franchise. But, the fact that he survived the destruction of the Buran after sacrificing its crew is shady, by even the broadest interpretation of what it means to be a Starfleet captain. In the Prime Universe, that is. That kind of thing would make perfect sense in the context of the "every man for himself" motto that the Terran Empire runs on. That's why we're convinced it's been Mirror Lorca captaining Discovery all along, just waiting for the right moment to get back home and finish his mission to overthrow the emperor -- something that would be much, much easier with a spore drive to help him.
For the entire first half of the season, Lorca has been doggedly pursuing the development of the mycelial drive, despite Stamets' objections and the ethical issues involved in using the tardigrade and, later, one of his own officers as pilots. He even signed off on Stamets performing the illegal eugenics therapy necessary to interface with the drive. Supposedly Lorca's sense of urgency came from his desire to win the war with the Klingons, but after episodes 9 and 10, it's impossible to ignore that he had an ulterior motive.
In the winter finale, "Into the Forest I Go," he reveals to Stamets that he's been doing his own private research on the spore drive all along, resulting in the discovery of how to use the mycelial network to master interdimensional travel. Lorca practically becomes giddy while discussing the scientific possibilities with the mycologist, but it's the first time he's shown any interest in scientific exploration. Even Stamets is surprised by Lorca's sudden interest: "Captain, I didn't know you cared." That's because Lorca doesn't care about scientific exploration outside of the spore drive that will get him back to the Mirror Universe and assist in his endgame (whatever that may be).
If we still haven't convinced you, the midseason premiere, "Despite Yourself," establishes that Lorca's Mirror Universe "counterpart" is supposedly dead and/or missing following an attempted coup and a pursuit by Mirror Burnham. If it were Lorca's plan all along to cross into the Prime Universe -- or even if he arrived there by accident -- he'd know he would require help if he wanted to return. Considering how vicious the missing Mirror Burnham is said to be, it would make sense to procure his own Burnham to assist in his return. Hence his move to bust her out of prison.
This way, he's able to take advantage of his Prime Universe crew and a Mirror Universe crew at the same time. To what end, we're still not sure. Is he part of the rebellion trying to overthrow the Terran Empire, or is he just another dissatisfied officer looking to kill his way to the top?
Airing Sundays at 8:30 p.m. ET on CBS All Access, Star Trek: Discovery stars Sonequa Martin-Green, Doug Jones, Jason Isaacs, Anthony Rapp, Shazad Latif, Mary Wiseman, Wilson Cruz and Mary Chieffo.