WARNING: The following contains spoilers for Star Trek: Discovery Season 3, Episode 9, "Terra Firma, Part 1," now streaming on CBS All Access.

Of the many twists and turns that came with Star Trek: Discovery's first season, one was the involvement of the Mirror Universe. Though the show's titular vessel spent only a fraction of its time there, the crew came back with a "souvenir" in the form of Terran emperor Philippa Georgiou (Michelle Yeoh). And she -- along with the Mirror Universe -- are the central to "Terra Firma, Part 1," the latest episode of Discovery.

"Terra Firma, Part 1" opens with Culber (Wilson Cruz) consulting with Mirror Universe expert Kovich (David Cronenberg) about Georgiou's condition. He reveals that what's happening to her is a symptom of traveling through both time and space, using a deceased "time warrior" from the Kelvin timeline as an example. He insists that searching for a solution is useless, and Georgiou should spend her final days sedated and confined to avoid hurting anyone. But it appears the Discovery's computer -- namely the sphere data -- has a different idea.

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According to it, a cure for her condition can be found on the planet Dannus V. Though it only increases her chance of survival by five percent, Culber feels this is another sign of the sphere data wanting to help the crew. Despite this new information, captain Saru (Doug Jones) initially refuses to go, as the Emerald Chain syndicate has begun military exercises and all of the Federation is on yellow alert. Surprisingly, Admiral Vance (Oded Fehr) goes over his head, approving the trip to Dannus V. In private, he uses this as a learning opportunity, telling the captain that letting a crew member die on his watch would change the way his crew look at him forever.

During the meeting, Vance pushes Michael (Sonequa Martin-Green) on being able to do what is needed and possibly let Georgiou go. It seems like Georgiou herself is not only fine with that prospect, but ready to greet her incoming death. She attacks Michael, trying to get her to kill her and die an honorable Terran death. But Michael counters it's not honorable to die as a Starfleet specimen and convinces her to explore the cure. Additionally, Georgiou invokes Michael's Mirror Universe counterpart, remarking how they both bend people to their will in different ways.

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The Discovery arrives at Dannus V, and Saru and Tilly (Mary Wiseman) bid a surprisingly emotional adieu to the Mirror Universe native. Michael and Georgiou beam down to a frozen wasteland and begin their trek to where the sphere data has pointed them. In the meantime, Michael brings up her Terran version, who Georgiou adopted from a scrap yard because of her independency. She reasons that Georgiou antagonizes her because of her guilt for killing her daughter, but Georgiou curtly refuses that. Any further discussion is stopped, though, when they find the "cure:" A man (Paul Guilfoyle) in a bowler hat lounging in a chair, with a door in front of him.

Back aboard the ship, Adira (Blu Del Barrio) is exhausted trying to pull a distress signal may be a major clue to discovering "The Burn." In general, they're in an emotional tizzy, as their boyfriend and previous Trill host Grey has not appeared to them in some time. Stamets (Anthony Rapp) tries to comfort them, reasoning he's doing what's best. Meanwhile, Book (David Ajala) approaches Saru, excited to assist the Federation after seeing them help save his home planet. And while the captain does not decline his offer, he advises that, much like the Discovery proper, Book must wait for his opportunity to prove himself.

Adira is able to compose themselves enough to isolate the distress signal and plays the message for Stamets, Tilly and Saru. It's from a Kelpien vessel that crashed in the nebula, on a mission to find a dilithium nursery. Rescue seems to not be coming soon, and judging from the radiation burns, the Kelpien may not last long. Seeing one of his own on the signal seems to put a pep in Saru's step. He sends Adira and Stamets off to find out more about the crashed ship, and even goes behind Vance's back in keeping his investigation a secret for now.

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Down on Dannus V, the strange man introduces himself as Carl, before trying to lighten the mood with some corny door puns. He's reading a paper with the headline "Emperor Georgiou Dies Horribly Painful Death" allegedly dated tomorrow. To prevent that future, he invites her to walk through the door. Michael refuses for Georgiou initially, very wary of the weird circumstances. But Georgiou curtly shuts her up, charging forward through the door with a single glance back.

That door seems to take Georgiou back through time and space. She's arrived in the Mirror Universe, on the day her palace vessel the Charon was christened. As she gets debriefed by Mirror Tilly (also known as "Captain Killy"), she begins to get her bearings. She realizes this will be the day that Gabriel Lorca attempts a coup, and the day Michael betrayed her mother and tried to take her life, only to lose hers instead. Seeing this as a second chance, Georgiou's motive is clear. Though this may weaken her to the loyalists, she is adamant to bring Michael back into the fold and spare her life.

And Georgiou gets that opportunity when she and Mirror Michael reunite in the ship's bar. Amongst the raucous knife throwing and electric arm wrestling, the two sit down and catch up. Georgiou brings up Lorca and his coup to gauge her daughter's reaction. But Michael denies it all, saying she grew bored of their previous affair and she will always stay in line. Their conversation gets interrupted when Michael attacks Saru, a Kelpien slave in this universe. Seeing a possibility, Georgiou intervenes and spares his life, taking him for her own possession.

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In private, the two talk. After Georgiou reveals a new sympathy for him based on her knowledge of his Prime counterpart, Saru opens up. Michael has believed that her mother has changed and become weak, which has turned her over to Lorca's side. Still insistent she can change the future, Georgiou recruits Saru as her eyes and ears to tip her off about any other insurgencies from her crew.

In the shuttle bay, the crew attends a performance telling the story of the Terran emperor, before formally christening the Charon. In her subsequent speech, Georgiou talks about strength requiring the will to do what needs to be done, and how they must attack enemies from within. Just then, she stuns the congregation by killing Mirror Stamets, who was intending to assassinate her. Michael is surprisingly the first to jump up and hail the Emperor after doing that, but is also the first to leave the assembly.

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It turns out she went aboard the Charon, where she is greeted by Tilly, Georgiou and four phasers. Georgiou tells her daughter she will forgive her if she confesses. But that just causes Michael to laugh in her face maniacally. She feels not only has her mother grown weak, but she has lived her life as a "tool" of the emperor, unable to stand on her own. She kneels, challenging Georgiou to execute her for her treason. In this moment, the Emperor finally goes through with what she wanted to do since she stepped through that door. She refuses to kill Michael, musing, "At this moment, our future is unwritten. Let's make it count, shall we?"

That's where the first part of the two-part "Terra Firma, Part 1" ends. It's unknown whether the episode will continue to stay entirely in the Mirror Universe, as it did for the episode once Georgiou walked through the door. But if so, how will the Emperor's choice affect this seemingly alternate timeline? And how can revisiting the past serve as this five percent cure that she needs at this moment. As the woman of the hour herself would say, the future is unwritten.

Streaming on CBS All Access, Star Trek: Discovery stars Sonequa Martin-Green as Commander Michael Burnham, Doug Jones as Commander Saru, Anthony Rapp as Lt. Commander Paul Stamets, Mary Wiseman as Ensign Sylvia Tilly, Wilson Cruz as Dr. Hugh Culber, David Ajala as Cleveland "Book" Booker, Blu del Barrio as Adira, Ian Alexander as Gray, Tig Notaro as Chief Engineer Reno and Michelle Yeoh as Philippa Georgiou. New episodes of Season 3 air on Thursdays.

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