Problems
- The diagram depicting the U.S.S. Defiant was not accurate, particularly the section depicting the alignment of the warp nacelles.

Factoids
- Culber refers to the Federation possessing a "Manchurian test" that is highly effective at detecting brainwashing, i.e. installation of commands or personality engrams underneath a functioning consciousness.

Remarkable Scenes
- Discovery jumping into the mirror universe and being attacked by Vulcan rebels.
- L'Rell activating Tyler's hidden programming.
- Tilly unexpectedly having to play captain and stumbling through the role with hilarious nervousness.
- Tilly: "Hello, this is Captain Tilly, what the heck—heck—hell—what the hell! Hold your horses!"
- Lorca retrofitting the U.S.S. Discovery into the I.S.S. Discovery.
- Tilly on her mirror universe counterpart: "She's terrifying. She's like a twisted version of everything I've ever aspired to be. I'm gonna have nightmares about myself now."
- Tyler killing Culber.
- Lorca being tossed into the agonizer booth.
- Burnham fending off her assassination attempt.

My Review
Dr. Culber, may he rest in peace, asked Lorca perhaps the episode's most important question: "Do you even want [Stamets] to get better? Or did you want all this to happen?" That seems like much more than merely the emotional conspiracy theory of a grieving lover given that the closing moments of the previous episode depicted Lorca pulling out a computer, going into the "encrypted" section, accessing navigational control, and engaging in some kind of spore jump coordinates manual override shortly before the Discovery ended up jumping to the wrong place. It seems likely Lorca wanted his ship to jump into the unknown to avoid having to return to starbase 46 and face Admiral Cornwell. It's perhaps also possible Lorca might even originate from the mirror universe and wanted to return home. After all, mirror Lorca was stated to have still been at large after his failed coup against the Emperor. What if he traveled to the prime universe and replaced the original Lorca? He even said "let's go home" shortly after inputting the override. If that is the case though, it would be odd for Lorca to almost blow his cover by trying to personally answer the hail from the I.S.S. Cooper rather than asking Burnham to look up who their alter egos were before speaking to anyone from the mirror universe.

By and large, this episode is charming enough to be quite effective in spite of being almost totally irrelevant to the show's otherwise total serialization of the war with the Klingons. Numerous small details stand out as highly amusing, ranging from the hilarious Captain Tilly (now we know why Stamets called Tilly captain in Si Vis Pacem, Para Bellum!) to the fleshing out of the backstories of various characters' mirror universe counterparts. It's fun to imagine Lorca staging an uprising against the Emperor and being put down by Burnham. It would be even better if the next episode establishes the Emperor as being a descendent of Hoshi Sato. Likewise, this episode teases us with the intriguing possibility of the Discovery itself having switched places with its mirror universe counterpart; a remarkably frightening possibility that would parallel the events of TOS: Mirror, Mirror quite well. One remarkably annoying detail about this distraction from the Klingon war though is it doesn't make a lot of sense why the crew of the Discovery didn't transmit the Klingon cloak breaking algorithm they've been working on long before they jumped. Why hoard the data from their superiors?

The only real advancement in the Klingon war story we get in this episode is Tyler's continued creepy behavior. In addition to killing Dr. Culber, he is depicted reciting a Klingon prayer with L'Rell after she activates his hidden programming. Something appears to go wrong though, as she exclaims in an exacerbated fashion that the prayer should've caused him to remember his "other name." The hypothesis that Tyler is Voq seems even more likely now, but it remains a frustratingly weak narrative choice to keep withholding this revelation from the audience for the reasons stated in the review of the previous episode.

Another detail that should give us pause in this episode is the decision to make characters from the prime universe aware of events which will befall the U.S.S. Defiant a decade or so in their future during TOS: The Tholian Web and later Ent: In A Mirror, Darkly. Assuming the crew of the Discovery makes it back to their universe, which seems like a safe bet, they will return with knowledge of the demise of the Defiant and its subsumption into the mirror universe before those events take place in TOS: The Tholian Web. It's hard to imagine why they wouldn't mention this to Starfleet so they could warn the Defiant and prevent it from being lost. There are some possible reasons: for instance, someone could invoke some prototypical version of the temporal prime directive as a reason to keep silent on it. Or perhaps Lorca and his crew will be concerned if they prevent the Defiant from being subsumed into the mirror universe, it will alter their own history by preventing them from being able to use the knowledge they gain from it to return to the prime universe. But regardless, the decision to work the events of Ent: In A Mirror, Darkly into the plot of this episode means they will have to very carefully button this up later to avoid a serious plot hole, which given this show's sloppy approach to continuity so far seems like wishful thinking.

Indeed, while it is usually best to confine criticism of the show's broader approach to continuity to separate, dedicated analyses rather than repeatedly rehash such criticisms in every individual episode review, this episode offers us a remarkable new irony on that front. Ent: In A Mirror, Darkly was perhaps the best prototype for what a modernized show set in the 23rd century should look like. That episode of Enterprise showed us how to update the production quality of TOS to look much better without violating established visual continuity. More recently, Rogue One showed us how it could be done just as effectively in the Star Wars universe. But Discovery has taken a much lazier approach. They cherrypicked the plot out of Ent: In A Mirror, Darkly, and deliberately discarded the episode's central feature: an admirably rigorous respect for visual continuity. It would be like if Rogue One had completely redesigned the storm troopers or Darth Vader "because it isn't the 70s anymore." Because of this, instead of getting something as carefully crafted and stunningly impressive as Ent: In A Mirror, Darkly or Rogue One, each episode of Discovery is an exercise in seeing which piece of established canon they'll lazily throw away next, which is incredibly sad and was entirely unnecessary. Doing almost anything else would've been better than this.

But that broader criticism of one of Discovery's central premises should not play a role in how we should judge this specific episode. And when you look at this episode on its own merits, there is a lot to love. In fact, oddly, some aspects of continuity in this episode are quite additive like Ent: In A Mirror, Darkly or Rogue One rather than destructive like Discovery too often usually is. A particular highlight of this episode in that regard is its potential healing some especially stilted dialog from TOS: Mirror, Mirror in which Kirk jumps to conclusions way too quickly about how they must've been transported into a mirror universe. Perhaps by then Kirk will have read about the Discovery's encounter with the mirror universe, so it won't be such an amazingly wild guess. Plugging a plot hole with prequel plotting is partly what made Rogue One such a fine film: it finally gave us a good answer as to why the Death Star had such an obvious flaw. Perhaps Discovery will give us an answer as to why Kirk could jump to conclusions so quickly about the concept of a mirror universe in TOS: Mirror, Mirror? It's nice that not all of Discovery's contributions to continuity are so overwhelmingly problematic. Let's hope they button up that Defiant stuff correctly.