The episode begins with a member of the crew coming across a chilling scene: a delirious Paul Stamets clutching the lifeless body of Hugh Culber. As the episode progresses, the Mirror Universe is further developed: Mirror Saru is a nameless slave, which could very well be the fate of many or all Kelpians in this xenophobic timeline. Traitors are transported into the void of space for crimes as small as not believing in the might of the Empire. The agony booths are back and as cruel as ever. Burnham struggles not to lose herself in the cruelty and sheer horror of this twisted universe.
Michael gives Mirror Saru a name, because names are fun and handy things to have, and she finally gets her hands on information that may help them get back to their own universe. The problem is, she has no way to get the information over to the Discovery without drawing suspicion from the stab-happy crew. Saru insists that she finds a workaround, for the good of the crew. Neither Saru nor Tilly inform Michael of Culber's fate, as Saru argues that she must complete her mission with as few distractions as possible. Tilly claims that medical science hasn’t done anything to help Stamets in his condition, but maybe the spores might help, and Saru agrees to try.
Michael receives a message from Captain Maddox of the flagship: they've found the base of the rebel leader Fire Wolf and the I.S.S. Shenzhou is tasked with its destruction. As she doesn’t necessarily want to murder the only hope for a peaceful future for this universe, she does her best to stall. Michael has a team assembled, but after consulting Lorca on the matter, he advises her to go to the surface with only Ash Tyler, so that their true intentions aren’t made immediately obvious. He also asks her to hurry. His extended stay in the agony booth is taking its toll.
While Tilly and Saru work on bringing Stamets back to this plane of existence, Michael and Tyler land on the planet. Michael immediately surrenders, and they are brought to the rebel base camp. Surprise of all surprises, Mirror Voq is the leader of the resistance. This revelation makes Tyler twitchy with unease.
Mirror Voq has Mirror Sarek perform a mind meld with Michael in order to uncover her intentions. During the meld, Mirror Sarek sees the universe she comes from, with it’s diversity and acceptance and abundance, and deems her trustworthy.
The rebels agree to evacuate before their base is blown sky high. In return for this forewarning, Michael asks Mirror Voq how he could look past all of their differences and make the resistance work. He responds by saying that being Klingon means fighting until the end, even if that means seeking and accepting the help of other races to ensure all of theirs survival.
The dialogue between Michael and Mirror Voq stirs something inside Tyler, and he attacks Mirror Voq. He calls Mirror Voq a disgrace in the ancient language of the Klingons, which confuses them all. Mirror Voq wins the fight handily and Michael pleads with Mirror Voq to spare his life, even though Tyler was the one to start it. With the exchange of rebel intel that is soon to be useless, they leave to begin the process of evacuating the planet. Back on the Discovery, Tilly and Saru continue to work on Stamets with use of the mycelium spores, but he ultimately flatlines, and not even the medical staff can bring him back.
Once more aboard the Shenzhou, Michael confronts Tyler about the stunt he pulled at the rebel base camp. She also brings up his recent behavior in general, which has been more than a little questionable. Through a series of repressed memories, Tyler realizes that his personality has been overlaid with that of Voq. Voq’s personality begins to inhibit Tyler’s body fully, and he claims credit for Culber’s murder, which Michael wasn’t even aware had happened.
A fight breaks out between Michael and Tyler/Voq, and she is ultimately saved by Mirror Saru and a few crewmember who are loyal to her. As a result of trying to murder the captain, Tyler’s immediate execution is ordered. Stamets, who continues to be dead but maybe not really, runs into Mirror Stamets somewhere in the mycelium network.
Michael personally conducts the execution of Tyler/Voq by transporting him into open space, but he is quickly saved by the Discovery. Tyler/Voq remarks that she should have let him die out there, but in truth, she placed the data file on his body so that it would safely reach the Discovery and they could begin the process of getting back home.
Michael has Lorca brought to her ready room for a friendly chat, Their chat is interrupted by an unidentified ship opening fire on the the rebel base well before they completed their evacuation. It is revealed that Mirror Georgiou is this Universe’s Emperor, and that she is behind the destruction as she has grown impatient with the pace the Shenzhou is operating at. Emperor Georgiou commands her to show some respect, and Michael bows.
Up Next: Lorca and Burnham meet the Emperor face to face!