Now that the Federation has acquired the missing data from Ni’var, Cmmdr. Michael Burnham (Sonequa Martin-Green) and the crew of the USS Discovery look forward to figuring out the source of the Burn. But first thing’s first, there’s a particularly homicidal Terran with a progressive brain condition on board, and as much as Dr. Hugh Culber (Wilson Cruz) reasons with her, Philippa Georgiou (Michelle Yeoh) is as ornery as ever, fighting him tooth and nail.
Book (David Ajala) comes to Michael for help with a complex problem involving his brother and the health of his homeworld, Kwejian. They go to Admiral Vance (Oded Fehr) for permission to assist, but the admiral is reluctant to spare the manpower to investigate. Sea locusts are destroying Kwejian agriculture and folks are starving, the Emerald Chain is exploiting their position. After weighing their options, he agrees to permit DISCO to escort Book in an observational capacity only with strict orders not to engage.
We finally meet the elusive Osyraa (Janet Kidder) everyone in this century has been so afraid of. Meeting with her nephew Tolor (Ian Lake), Osyraa learns that Ryn (Noah Averbach-Katz) has escaped with Book. She transports him into a nearby trance worm cell to be eaten alive, ignoring his pleas for mercy.
(Acting) First Officer Ensign Tilly (Mary Wiseman) settles in nicely in her new position, even going so far as to help Saru determine a new jump command term. Together, they meet with Lt. Stamets (Anthony Rapp) and Adira (Blu del Barrio). There, they expose the root of the biggest problem in the galaxy, the origin of the Burn. The Verubin nebula is a nasty one, but they work together and uncover a new fact: the tune everyone’s been humming is actually a distorted Federation distress call. Stamets volunteers Adira’s skills to help decode the encrypted message within the call. When Saru and Tilly leave, Adira asserts their gender neutral pronouns (finally!), and their new FoundDad accepts them with grace.
On their way to the bridge, Burnham addresses the pink elephant in the room, and asks about Book’s brother. He clarifies the relationship, including the part where his brother began selling trance worms to the Emerald Chain and the animosity that came with that decision. Burnham is in full support mode, and assures him that they’ll find a solution.
DISCO jumps to Kwejian and hails the planet. Book is clearly stressed when they get no response, and long-range sensors pick up a heavy cruiser 30 minutes out. Book knows it’s the Viridian, Osyraa’s ship, and Saru orders Burnham to escort and observe to determine if DISCO or the Federation can be of assistance.
Meanwhile, Georgiou joins Dr. Culber and Dr. Pollard (Raven Dauda) in sick bay for her appointment. She lets off a couple rounds of insults, but at this point, the doctors are prepared and quickly sedate her to begin their scans.
Stamets and Adira kill some time in a tender moment as their algorithm works on the encrypted distress call message. Adira reveals that they haven’t heard from Gray, and their struggle to adjust to having the memories of so many people within them. Stamets consoles them, offering to accompany Adira’s cello with his piano as they wait for the calculations to complete.
Saru and Tilly confer over the whereabouts of Burnham and Book in his ready room as Ryn bursts in. Tilly’s on it, correcting his conduct immediately. He yields, but remains obstinate, declaring his distrust of the Federation as he insists that he helps Book with his task. Saru reminds him that he’s not a prisoner, and Tilly informs him that the Emerald Chain is en route to the planet. Ryn relaxes considerably, and focuses again on helping Book.
On the planet, Book explains the plague of the sea locusts while Burnham is dazzled by the beauty of the sanctuary. They’re quickly intercepted by a group of armed people, led by Book’s brother Kaheim (Ache Hernandez), and after a few fraternal jabs, are taken away.
Back in sick bay, Georgiou has another episode in the middle of her scan, and Culber and Pollard scramble to keep her alive. We see flashes of light and glimpses of a traumatic event as the doctors work on her. We also see some sort of temporal shift before she wakes up, and while she hops out of the bed in denial with a stolen cerebral monitor in hand, Georgiou is clearly shaken.
On Kwejian, Kyheem and Book bicker as Burnham looks on. We discover that Kyheem and other family members in fact work for the Emerald Chain, to the point where he’s asked Book to give up Ryn to Osyraa.
In orbit, the Viridian arrives and openly scans DISCO. Saru patiently stalls Osyraa as they try to contact Burnham, but she’s not having any of it, giving them five minutes to turn over Ryn before they open fire on Kwejian. Osyraa then contacts Kyheem and pressures him to give up both Book and Ryn. When he refuses, she opens fire on the planet. For the time being the atmospheric shielding holds, but Book and Burnham scramble to get to safety.
On DISCO, Ryn refuses to tell the crew why Osyraa is so obsessed with him, and continues to try and contact Burham on the surface. Georgiou tries to access the data from her scan as the ship goes to red alert, and Culber intercepts before she can make a mess of things by running after Burnham.
Tensions mount as Osyraa continues her assault on Kwejian’s defense systems. Both DISCO and Burnham are struggling to contact each other amidst the barrage of weapons fire, and Saru checks in with Ryn for intel on the Viridian inself. Realizing that DISCO can’t get involved, Tilly suggests a skilled pilot take a non-Federation ship like Book’s and attempt to disable the Viridian. All eyes are on Lt. Detmer (Emily Coutts), and paired with Ryn, they set out on Book’s ship. Detmer struggles with automated controls and decides to take full manual control, showing us exactly why she got into Starfleet. They share a beautifully encouraging moment and manage to take out critical weapons systems on the heavy cruiser just in time to save the planet.
On the surface, Book and Burnham are once again intercepted by captors led by Kyheem. The brothers finally fight it out, and Book manages to subdue Kyheem, convincing him to resist the Emerald Chain. Burnham proposes that they attempt to move the sea locusts together, but the brothers insist that the numbers are too high for just two empaths. Burnham offers the Discovery as a means to amplify their empathic signal, succeeding in returning the locusts to their natural habitat.
When the dust has settled Detmer brags to the rest of the bridge crew about piloting full manual. Tilly comforts Ryn, encouraging him and his bravery in standing up to Osyraa and the chain once again. She also has a chance to clear up the prejudices Ryn has about the Federation. Ryn confides that the Emerald Chain is running out of dilithium, and Osyraa wants Ryn dead because he knows. Book and Kyheem reconnect and heal old wounds, and Stamets and Culber dote over Adira. Book finally admits to his appreciation of the Federation, and Burnham sets off to repair his ship.
It’s great to finally learn Book’s origin story, but with it brings new issues. Osyraa and the Emerald Chain hang ominously on the outskirts of further storylines, pressure mounts as the crew gets closer to solving the cause of the Burn, and Georgiou’s condition is getting progressively worse. Will their newly-strengthened bonds help the crew of the Discovery to deal with whatever comes next? Will it be enough? Does Adira know something about that signal?