WARNING: The following contains spoilers for Star Trek: Discovery Season 3, Episode 8, "The Sanctuary," now streaming on CBS All Access.

In last week's episode of Star Trek: Discovery, Michael Burnham (Sonequa Martin-Green) explored the concept of "home,"  revisiting the planet she grew up on and contemplating her role on the titular ship's crew. In the show's latest episode, "The Sanctuary," it's her new boyfriend Book's (David Ajala) turn, as the show delves more into him by focusing on a rather interesting chapter in the mysterious character's life.

Before that, though, "The Sanctuary" opens on another lingering character mystery. Georgiou (Michelle Yeoh) talks with Culber (Wilson Cruz), and it's assumed that she's seeing the medical officer to talk about the flashes of Terran memories she's experienced the past couple of episodes. She proves to be one stubborn patient, however, attempting to still maintain a position of power. Culber is able to dish it right back to her, though, directing her to an atomic scan while warning her that without intervention, her brain could deteriorate past the point of no return.

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Meanwhile, Book seeks out Michael to share some urgent news. His brother has sent him a message that his home planet, Kwejian, is under threat from the Orion-Andorian syndicate known as the Emerald Chain. As Book explains further in Vance's (Oded Fehr) office, environmental changes following "The Burn" caused the planet's sea locusts to take to land and destroy their food supply. The Chain offered repellent in exchange for access to their trance worms, but it seems they want something more now. Despite Vance's reservations, Michael and Captain Saru (Doug Jones) are able to get Discovery to go on the mission under a more diplomatic banner.

But we soon see diplomacy will not work with the Chain, as we finally meet its leader: Osyraa (Janet Kidder). She's confronting her nephew Tolor (Ian Lake) about the prison break that happened on Hunhau, with a particular fixation on Andorian escapee Ryn (Noah Averbach-Katz). True to her reputation, Osyraa proves herself to be merciless. As punishment for his slip-up, she arranges for Tolor to be eaten by a trance worm, something she did to his father years ago.

Back aboard the Discovery, Saru and new first officer, Tilly (Mary Wiseman), are trying out new catchphrases as they walk into engineering. There, Stamets (Anthony Rapp) and Adira (Blu Del Barrio) present the data about "The Burn" they've acquired from Michael. The origin of the event seemed to be in the Verubin nebula, which is giving out an audio signal similar to the song we've heard in previous episodes. They also isolate the noise and find a Federation distress signal in it. As Stamets convinces Adira to write an algorithm to decode it, they reveal in private their preferred pronouns. While it's an extremely vulnerable moment for the young genius, their new friend is incredibly accepting, giving a simple nod and a smile.

Book is nervous about going back home, namely because of his brother. Though not biological, the rift that developed between them still hurt when he started hunting trance worms for the Chain. He's not looking forward to showing his new beau what has become of his planet. When Discovery jumps to Kwejian, Saru decides to beam the two of them down to inspect the situation, while they deal with the incoming Osyraa problem.

Elsewhere, Adira is mournfully playing cello when Stamets finds them. They reveal that deceased boyfriend and previous host Grey hasn't spoken with them recently, fearful he is hiding. In general, Adira is undergoing a literal identity crisis, not sure who they'll wake up as every day. As Stamets tries to put her mind at ease with a duet, Ryn causes some discord as he storms into Saru's office, demanding he leave the ship and grumbling that Federation favors often come with strings attached.

Kwejian turns out to be a serene autumnal planet, much more natural than urban. Even the pesty sea locusts have a bright turquoise glow. But the calm is interrupted when Book and Michael get captured by a group of people, including Book's brother Kyheem (Ache Hernandez). They're taken back to his home, and you could cut the tension between the brothers with a bat'leth. Kyheem accuses Book of leaving his planet and family behind, while Book chastises him for working with the Chain. Kyheem reveals the reason behind his hail; Osyraa knows Ryn escaped with Book. And without him in her possession, she may destroy Kwejian in retribution.

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In Sick Bay, Georgiou goes through the rare outfit change for her atomic scan. But as the scan goes along, things are far from routine. In the middle of it, she comes to, on the verge of cerebral hemorrhage and having emotional flashes from the Mirror Universe. Her body even begins to get affected, almost like she's being pulled somewhere else. Her reveries literally break the scan, but she tries to recover by walking away and denying anything had happened.

Osyraa's ship arrives, and the Emerald Chain and Discovery leaders come holo-face-to-face. While Saru tries to keep a straight face through diplomatic protocols, the Orion shoots him down, talking about the "hubris" of the Federation. She threatens them to give her Ryn, or she will take it out on Kwejian. She next talks with Kyheem, who is brooding after nearly coming to blows with Book. She points out that the sea locusts could destroy their food again without the Chain's help. Despite all this, Kyheem refuses to give up Book. And true to her word, she begins carpet bombing Kwejian.

As the planet goes up in flames around them, Book and Michael scramble to bring up its defense systems. What doesn't help is Kyheem, who intervenes to scrap it out with his brother. Above Kwejian, Tilly comes up with a plan to save the day. With knowledge of how to destroy Osyraa's ship, Ryn takes off in Book's non-Starfleet ship alongside Detmer (Emily Coutts) to stop her. It's a big testing moment for the pilot, who has seen her confidence shaken throughout the entire third season. But despite her reservations, she literally takes control and does some incredible flying, piercing Osyraa's defenses and taking out a good chunk of her ship. The Discovery emerges victorious, but before leaving, Osyraa promises them the Federation will feel the full weight of the Chain.

Back on Kwejian, Book challenges Kyheem to kill him, but his brother can't go through with it. After Osyraa leaves, Kyheem laments his situation, revealing he has a son. While Book is reeling in surprise, Michael comes up with a plan to save the planet. With their combined empathic powers, as well as a little help from Discovery, they are able to encourage the sea locusts to go back to the water. The brothers finally see eye to eye, and Kwejian is famine-free as a result.

As Detmer gloats about her badass maneuvers in the cafeteria, Tilly sits down with Ryn. While he's grown up with rumors of a deceitful Federation, he finds her trusting enough to tell her that that the Chain is running out of dilithium. The reason he was so valuable to Osyraa is because he knows her big secret.

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Meanwhile, Book and Michael give Kyheem and his son a tour of the ship. The brothers jokingly banter before thanking each other for doing what they needed to do for Kwejian. In private, Book admits to Michael that the day has made him see the Federation in a new light, considering what it can do for planets in need. And surprisingly, he wants in! As Michael walks off to fix his ship, she has a smile on her face, telling him how much she liked visiting his home.

While "The Burn" still remains the big mystery of the season, "The Sanctuary" hypes up the Emerald Chain as the big bad. After several mentions, Osyraa finally gets introduced, and she's even more blunt and ruthless than expected. But generally, this episode showed that every veneer has cracks. Whether it's Osyraa or Georgiou, despite the front, weaknesses still exist to prove they're only human (or Orion). It remains to be seen whether these characters will withstand these faults, or, to use Saru's new captain's quote, "carry on."

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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