On September 4, 2018, Monica settles into a routine in Cambridge. She spends her days coding for EMBRS, running errands for her grandparents, and messaging Louise. One day, her grandmother asks to see the pencil she gave Monica and explains the family’s secret power of Reforging, which she describes as reviving a story to understand a writer’s words exactly as intended. Then, without warning, she inserts the pencil into her wrist. The heart melts into her bloodstream, and her phoenix scars pulse and darken.

When her grandmother opens her eyes, Monica realizes she now knows everything Monica wrote about, including her feelings for Louise. This is how Monica unintentionally comes out. Her grandmother bleeds black ink onto a notebook, recreating Monica’s drawings and a line expressing how powerfully Louise affects her. Then she asks about Louise and suggests inviting her over.

Overwhelmed by her grandmother’s acceptance, Monica cries in her embrace. She asks if her grandmother will forget this moment because of her illness. Her grandmother promises she won’t, though the promise sounds like a plea.

In the present, Yun regrets Reforging Monica’s pencil without her permission, recognizing it parallels a past wrong against Meng.

The story flashes back to the early 1940s. To reduce the suspicion on their family while their husbands fight the Japanese, the girls’ mothers pretend that Meng is Yun’s sister and that Yun’s father died many years ago. Despite this, collaborationist police frequently harass them. One night, the girls sneak to the workshop, and Yun Reforges a spy’s pencil, a traumatic experience in which she witnesses the story of a young woman who joined the resistance and was raped and murdered. Meng comforts her.

In early 1942, resistance member Mr. Gao demands they use Reforging to pass coded messages, threatening to expose Yun’s father and the rest of their family if they refuse. Yun’s mother agrees. To cope, the girls continue writing their shared story. When Meng realizes their anti-Japanese tale is dangerous, she crumples the pages. Yun retrieves and burns them, then devises a safer method: They’ll take turns writing illegibly over newspaper, pass the pencil to Reforge, then destroy all evidence so the story exists only between them. Meng agrees, and they promise to stick together.

On September 13, 2018, Monica feels uneasy knowing her grandmother can access her private thoughts through her writings. When she asks her grandmother to Reforge Meng’s pencil, her grandmother refuses and becomes agitated.

On a visit to Chinatown with her grandfather, Monica learns he’s known about Reforging for about 70 years. Later, Professor Logan asks to use the story of how EMBRS reconnected Monica’s grandmother with Meng and requests that Monica give his students a coding demonstration.

Louise calls to thank Monica for the meatballs. Monica tells her about Reforging, and Louise surprises her by finishing Monica’s explanation of the process. Louis explains that Meng had told her about the power, though she hadn’t fully believed it. When Monica asks if Louise only befriended her because of her grandmother’s power. Louise admits initial curiosity but insists she continues talking to Monica because she likes her.

Later, Monica tells her grandmother that Louise knows about Reforging. Her grandmother proposes a trade: She’ll Reforge Meng’s pencil once Monica invites Louise to visit. Monica agrees.

In the present, Yun fears her memory loss will leave only the mechanics of Reforging, causing her to relive others’ stories long after her own is gone. She plans to ask her husband to keep pencils away from her if this happens.

The narrative flashes back to the Japanese occupation. Reforging non-Phoenix pencils is dangerous, and one attempt leaves Yun’s mother incapacitated for a week. Over three years, Yun and Meng Reforge coded messages for the resistance nearly every night, their phoenix scars deepening.

When Yun is 17, Meng learns her father has died in battle. Meng’s mother begins a relationship with Mr. Gao, which angers Meng but helps secure supplies and protection for the family.

After Japan’s surrender in 1945, a boy asks Meng to go out with him. As Meng prepares for the date, the girls’ mothers allude to another method of Reforging that’s pleasurable instead of painful. They refuse to explain further, warning only that her arm must be clear of any un-bled Reforgings before she meets the boy. The chapter ends with Yun resolving to explain this alternate method to Monica.

On September 22, 2018, Monica describes her grandmother’s worsening condition. Her grandmother expresses guilt over Reforging Monica’s pencil without permission and asks if Monica still wants to learn about the family’s power. Monica asks for more time to decide and uses EMBRS and cleaning as outlets for her worries about her grandmother.

Monica’s coding presentation for Professor Logan succeeds, and he praises her as the most talented sophomore he’s worked with. Louise watches the recording and tells Monica she looks cute.

When Louise sends her thesis proposal for her new major, Monica realizes the project focuses on her grandmother’s generation of Shanghai women and feels used. Sensing her discomfort, Louise reaffirms her personal interest in Monica, and they share a mutual coming-out moment discussing their first kisses. Monica resolves to distance herself, but her resolve breaks when Louise sends her vacuum filters with a sweet note.

Spurred by her grandmother wanting a fourth player for mahjong, Monica invites Louise to visit. Louise immediately accepts and schedules a visit for her upcoming fall break. Monica tells her grandmother she’s fulfilled her end of their deal, but her grandmother insists she’ll only Reforge Meng’s pencil after Louise actually visits.

In the present, Yun describes Monica’s frantic preparations for Louise’s visit and admits she can’t recall Meng’s postwar boyfriend’s name or appearance.

The narrative flashes back to late 1945. Meng begins dating regularly and grows distant from Yun, who is now 19. Mr. Gao brings news that Yun’s father is returning. He also brings more pencils for the women to Reforge, as the Nationalists are now fighting the Communists and prefer to use the same covert means of communication they favored during the Japanese occupation. Meng reverts to her own surname and spends most afternoons away. Yun’s old jealousy resurfaces.

One night, Meng cryptically mentions discovering the other way of losing a Reforging but refuses to explain. Feeling excluded, Yun tricks Meng’s boyfriend into letting her inspect his pencil and secretly swaps it for a different one. Alone, she Reforges it and experiences his intimate, desire-filled poems about Meng. Consumed with guilt, she bleeds the poems into a notebook but doesn’t have time to burn it.

Later, Meng silently slips Yun a pencil. Fearing discovery, Yun Reforges it and finds only the next chapter of their shared story. She joins Meng in the workshop and helps with Meng’s portion of the Reforging. Although Yun doesn’t apologize for what she did, she feels close to her cousin again. She understands for the first time that some stories aren’t meant to be shared. She reflects that this was their last peaceful moment before the next war separated them.