Culber observes signs that the holo program is breaking down. Saru tries to talk to Su'Kal about the radiation poisoning affecting him and Culber. Culber advises him. Adira arrives and gives them the radiation meds they brought with them.

Gray comes in and Saru and Culber are able to see him.

At Federation HQ, the Viridian fires on the shield from the outside while Vance plans an attack on the Discovery. Kovich stands nearby and questions his tactics.

Osyraa has Aurelio prepare a truth serum for Book and plans to have him take them to the dilithium planet. Zareh brings Burnham to the bridge where Osyraa slaps her for the trouble she's caused.

Reports of Tilly's group come in from Deck 7. Osyraa orders all her minions to Deck 5 and above and sends Book to Sick Bay.

Osyraa shuts off life support on the decks below Deck 5, trapping Tilly and the rest while the oxygen vents.

The Federation's shields are about to fail. Stamets arrives and begs Vance to send him back to Discovery so they can rescue Saru, Culber, and Adira.

As the shields go down, Ni'Var's fleet arrives to help the Federation. Osyraa issues orders to the Viridian to jettison its pesticides to poison the ships' crews. Burnham offers to convince Vance to stand down.

Burnham talks Vance into letting Discovery and the Viridian go. Osyraa refuses to return life support to the lower decks and orders Burnham off the bridge.

In the nebula, Saru offers to make a traditional Kelpian meal with Su'Kal in order to form a connection and tries to convince him that he is, in fact, Kelpian.  Su'Kal leaves him for a time.

The truth serum doesn't work on Book and Zareh insists on using a neural lock. Aurelio protests but Osyraa overpowers him and knocks him out. Zareh puts the neural lock on Book and begins to torture him to make Burnham help get him to give up the flight path through the nebula.

Su'Kal shares his fears with Saru. He insists that Saru explain why the Federation never came for him. Saru explains the Burn and the holo program created by Su'Kal's mother.

Burnham gets close to Book under the pretense of convincing him to give up the information but she injects him with adrenaline and triggers a quarantine field so they can escape.

Tilly's team is trying to bypass the life support shut down. Owo shares that she can hold her breath for a long time from childhood training.

Burnham opens a ship-wide channel and makes a coded announcement for Tilly's benefit. Tilly interprets it correctly that Burnham wants them to sabotage a nacelle to force the ship out of warp.

Su'Kal returns and tells Saru that all the holos are gone. Saru explains the choice he had to make to leave safety. The folktale creature appears and frightens Su'Kal.

Culber, Gray, and Adira find an open edge to the holo. Culber says he can't explore it because the radiation is too powerful. Gray, not being corporeal, offers to go investigate what is outside the holo. While he's gone, Adira and Culber discuss Su'Kal.

Su'Kal discovers the elder holo is also gone. Saru offers to be a source of comfort and support.

As the team starts to suffocate, Tilly tells Owo to complete the mission and leave them behind.

Burnham hacks a turbo lift but isn't able to move it. She and Book climb onto the outside of the lift to trap and attack the regulators. She jumps onto another moving lift, hijacks it, and rides it to the data core where Osyraa and her regulators are waiting.

Owo sets the explosive in the nacelle but can't make it back out. A DOT-23 containing the sphere data tries to encourage her to stand but cannot enter the nacelle itself without being dstroyed.

Discovery drops out of warp when the nacelle blows. Osyraa orders the Viridian to bring the Discovery into the loading bay.

Zarah insults Grudge and Book throws him out of the turbo lift.

In the fight with Osyraa, Burnham is thrown up against a block of programmable matter which Osyraa shoves her into, assuming she'll suffocate. Burnham emerges, weapon first, and kills her. She commands Discovery to reset, restoring life support to all decks and beaming all regulators off the ship. She calls all crew to report to the bridge.

Owo wakes up, having been saved by the DOT-23 which powers down due to the damage it sustained.

Tilly gives up command so Burnham can lead them out of the Viridian. She plans to eject and explode the warp core and use Book to navigate the spore drive to the nebula before they blow up too.

Su'Kal is afraid to turn off the holo but Culber and Saru reassure him and he enters the locked door. The computer plays back his mother's death which caused him the distress that triggered The Burn.

Gray freaks out when he realizes that he'll disappear when the holo is shut off. Culber promises that he and Adira will find a way to make Gray visible again.

Once the holo is off, Su'Kal can see that Saru is actually Kelpian.

Burnham's plan works although Book's navigation takes a frightening amount of time.

Saru plays Su'Kal's mother's final message and the Kelpian ship is about to collapse when Discovery makes contact and beams them out.

In the epilogue, the sphere data DOT-23 is repaired by Owo and Jett. Stamets isn't ready to forgive Burnham yet. Osyraa's death ends the Chain's power and planets are returning to the Federation. Saru returns to Kaminar with Su'Kal.

Burnham runs into Sahil, now a lieutenant, when she meets with Vance about becoming captain of Discovery. It's Saru's wish and Vance's recommendation as well.

Burnham takes command and Discovery leaves to deliver dilithium to various planets.