Stardate 865211.3: Burnham records a message for Discovery detailing what she has learned in her year in the future.
Dilithium supplies dried up 700 years after they jumped through the wormhole. New warp designs were unreliable. Then The Burn happened and every ship with an active warp core detonated, destroying the Federation. She has been working as a courier, trading for information about the Federation and The Burn. She has grown to accept she may never be reunited with Discovery. She contents herself with her new life and her friendship with Book.
When the signal comes through from Discovery, she rescues them and then beams aboard. The crew welcomes her affectionately but Georgiou holds herself aloof.
Burnham and Saru discuss the situation. Burnham reveals that she had sent a message to Terralysium and they responded months later with no knowledge of her mother.
Burnham debriefs the bridge crew on the devastation caused by The Burn. She also lets them know she found a twelve-year-old transmission from a Federation Admiral, Senna Tal, calling any Federation crew back to Earth. She suggests they use the spore drive to return to Earth and see if they can find Tull.
Saru initiates a discussion about the role of captain but Burnham immediately insists that he take command.
Tilly tends to the wall of fallen comrades, mourning them. Burnham checks in on her. Tilly expresses the loss she feels for the family she left behind. She hopes there's something on Earth that they'll recognize still. She guesses that Burnham had to let go of her hope to see Discovery and its crew again, bringing Burnham to tears.
Book beams aboard, greeted by Georgiou whom he views with caution.
Burnham gives Book dilithium for his part in reuniting her with Discovery. She offers him the chance to come with them to Earth for a clean slate.
She proposes Discovery hides their dilithium stash on board Book's ship which can cloak its existance. Saru questions her judgement and wonders how much she's changed. He wants to offer her the position of First Officer but wants her to explain herself if possible.
Book's ship will stay in the shuttle bay to hide the dilithium. Book joins them on the bridge for the jump to Earth.
As they approach Earth, Saru notices arrays in orbit and they turn out to be forcefield generators. Two non-Federation ships approach Discovery. They are hailed by Captain Ndoye of the United Earth Defence Force who accuses the Discovery of violating their regulations and she orders them to leave immediately.
Saru presents themselves as Starfleet, covering for their ship's obvious age and the fact they were not affected by The Burn. Ndoye tells them they must be inspected before they can come any closer to Earth. They beam aboard immediately and aggressively, catching the crew off-guard.
Burnham sets Book up with a uniform so he can pose as part of the crew. Book is not impressed with the plan.
Georgiou makes observations to Burnham that she has changed and may never be comfortable aboard Discovery again.
Saru and Burnham listen to Captain Ndoye describe life on Earth after The Burn. She informs them that they are constantly attacked by dilithium raiders, currently led by someone named Wen. She also reveals that Starfleet was expelled from Earth a hundred years before. Furthermore, her records show that Admiral Tal died two years previously.
The inspectors in Engineering include a sixteen-year-old named Adira. She has many questions about the spore drive chamber.
Red alert sounds as Discovery is approached by five raiders, led by Wen. Ndoye wants Discovery to leave immediately so her forces can deal with Wen. However, they are unable to transport off the ship. She accuses Saru of sabotage.
Burnham finds Book and recruits him for her plan.
Tilly and Stamets find tech installed by Adira to block the beaming frequencies of the inspectors.
Book's ship leaves the cargo bay and Saru realizes they've taken all the dilithium with them straight to the raiders. Ndoye orders her ships to target Book's ship.
Burnham offers the dilithium to Wen on the condition he leaves Earth's orbit. She's betting on Saru covering them from an attack from Earth's forces.
Ndoye's ships fire. Saru orders the Discovery move them to take the hit. They lose shields from the barrage.
Burnham convinces Wen to lower his shields to receive the dilithium.
Discovery prepares to take another hit but Book's ship suddenly cloaks and the raiders power down their weapons.
Burnham and Book bring Wen onto the bridge and insist on a parlay with Captain Ndoye. The talks begin badly but Georgiou unmasks Wen, revealing that he is human.
Adira is in the Jeffries Tubes and Stamets tracks her down. She asks about the spores and he explains the spore drive and his role as navigator. He also explains that they are time travellers.
Adira reveals that she became an inspector in order to find a Starfleet ship. She claims to know Senna Tal.
Wen explains that they are from Titan and a disaster wiped out their ability to sustain themselves. When they sent a ship to Earth, they were fired upon and this instigated the raider attacks for dilithium. With Saru and Burnham facilitating, the two sides begin to discuss terms.
Ndoye agrees to let Adira stay with Discovery. Adira and Saru discuss her connection to Tal and she reveals that she carries the Tal symbiont even though she is not Trill.
Burnham and Saru debrief and she admits she should have discussed her plan with him. She accepts his position as First Officer but cautions that she needs time to readjust to life on Discovery.
Burnham and Book bid farewell.
Saru gives the crew leave to visit Earth and they find a tree that was on Starfleet Academy campus, now enormously huge.