Georgiou is being examined by Dr. Culber and not cooperating much. She eventually submits to a scan and Burnham checks in only to be rebuffed. In the corridor, Book runs up to Burnham and tells her he needs to return to his home planet because of Osyraa. Burnham takes the problem to Vance and Saru.
His homeworld gave up their trance worms to the Emerald Chain in exchange for a sea-locust repellent to save their harvest.
Vance says over fifty worlds are in the same predicament as Book's homeworld. Saru proposes Discovery become an "observer" to the conflict in order to transport Book home quickly.
On Hunhau, Osyraa receives a report from her nephew, Tolor. She feeds him to a trance worm for losing Rin, Book's Andorian friend.
Tilly reports to Saru regarding the ship's status. Saru is also looking for a captain's catch-phrase.
They join Stamets and Adira and are informed that they've combined the Ni'Var data with Burnham's and found the source of the Burn, the Verubin Nebula, from which a signal is emitting. The signal sounds like music and it is the song that has been encountered in multiple places. Saru analyzes more of the audio signal and removes the distortion, revealing a Federation distress signal. Stamets volunteers Adira to write an algorithm to decode the signal.
Adira tells Stamets that they would prefer to not be referred to as "she/her", feeling the pronouns "they/them" are more accurate.
Book is anxious about bringing Burnham to his homeworld.
They jump to Book's homeworld and find no response to their hails. Osyraa's ship is en route. Saru suggests that Book and Burnham beam down to the planet and try to learn what is going on.
Georgiou returns to sickbay for her scan.
Adira is playing the cello and Stamets orders up a piano so he can accompany her. Adira reveals that Gray's not talking to them anymore and they don't know why.
Tilly and Saru are tracking Book and Burnham when Ryn bursts into the ready room. He wants off the ship but is taken aback to hear that Osyraa's on her way.
The planet has a shielded zone where signals are scrambled and people can't be tracked or beamed in or out. Book calls it The Sanctuary. The area is rife with sea locusts but Book is able to emphatically clear a path for them. While Burnham revels in the beauty of the planet, Book realizes that they are surrounded. His brother and a group of armed soldiers take them prisoner.
During the scan, Georgiou begins to have another episode. She physically begins to splinter. When she regains consciousness, she lies about her experience and steals one of the scan readers.
Book and his brother, Kaheem, reacquaint themselves. Burnham introduces herself. Kaheem tells Book that Osyraa wants Rin.
Osyraa's ship arrives and she and Saru introduce themselves. Osyraa demands Ryn be turned over. She threatens the crew and the planet if her demands are not met.
Osyraa and Kaheem talk. She wants Book and Burnham turned over as negotiating leverage for Ryn. She threatens famine for the planet, pointing out that Kaheem's son will starve to death. She fires on the planet to motivate Kaheem, targeting the defense system.
Saru intends to fire on Osyraa to prevent her from destroying the planet. He calls the crew to red alert.
Georgiou hacks her scan chip. Culber finds her and she confronts him with the knowledge that she's dying. He insists they talk.
Burnham and Discovery are unable to communicate. Burnham and Book are running to try to restore the defense system. Discovery can't see any weaknesses in Osyraa's ship but Rin states he knows where they are. Nilsson warns that if Discovery fires on Osyraa, it'll be seen as a declaration of war. Tilly suggests that Detmer and Ryn use Book's ship to disable Osyraa's ship instead.
In the presence of Ryn's fear, Detmer finds her confidence and becomes the pilot she was. She takes manual control of Book's ship and, following Ryn's instructions, takes out Osyraa's weapons and shields.
Burnham and Book are surrounded by Kaheem's forces but the shockwaves from Osyraa's attack knock them out and Book and Burnham escape. Kaheem comes after Book himself. Realizing Kaheem knew he was calling Book back to a trap, Book offers Kaheem the chance to shoot him point-blank but Kaheem can't pull the trigger.
With Osyraa's ship incapacitated, Saru offers assistance and Osyraa responds that she will bring the Chain down on Federation forces everywhere. She leaves.
Burnham convinces Book and Kaheem to combine their empathic powers to move the sea locusts out to sea. With Discovery amplifying their message, it works.
Back aboard Discovery, Detmers is full of confidence to Owo's joy and dismay. Tilly sits down with Ryn and he reveals that he knows that The Chain is running out of dilithium and that's why Osyraa wants him back.
Burnham and Book show Kareem and his son, Leto, around the ship. Book and Kaheem part on good terms.
Culber comes to bring Stamets to bed and they discuss Adira before she wakes up and she goes to her quarters.
Book and Burnham discuss his place on Discovery. He wants to be a part of the good they are doing.