Lily returns to her apartment after learning that Ryle will stay overnight at the hospital following a successful cranial separation surgery. Lily tries to calm herself with routine and reading, but thoughts of Ryle, Atlas, and the instability of her own certainty overwhelm her. Lily puts away the book Atlas gave her and chooses to read the final journal entry she ever wrote about Atlas, hoping to close that part of her life.

In the journal, teenage Lily writes to Ellen about her sixteenth birthday, which came forty-two days after Atlas left for Boston. Lily was miserable until Atlas appeared at her bedroom window that night. Atlas tells Lily he returned because she is still his favorite person, then reveals that the first night he stayed in the abandoned house, Atlas had gone there intending to kill himself. Seeing Lily in her bedroom gave Atlas enough feeling to keep living, and Lily’s later kindness helped save him.

Atlas explains that he is leaving for the military earlier than planned and does not want Lily to pause her life for him. Atlas promises that if his life ever becomes good enough for Lily to be part of it, Atlas will find her, though he asks Lily not to wait. The two share an intimate farewell, Atlas tells Lily he loves her, and Atlas gives Lily a Boston magnet that says everything is better there.

The night turns horrific when Andrew enters Lily’s room, finds Atlas in Lily’s bed, and beats Atlas with a baseball bat. Police and ambulances arrive; Atlas is taken away badly injured, and Lily has a panic attack. Andrew is not arrested, and the town treats Andrew as a protective father while condemning Atlas as a homeless boy who manipulated Lily. Lily writes that she has not heard from Atlas since and has been barely staying afloat.

Back in the present, Lily confirms the journal entry was her last letter to Ellen. Lily later learned that Atlas survived and joined the military, but Atlas never contacted her, and she never fully stopped loving him. Lily reflects that Boston partly drew her because of Atlas and partly because she wanted to escape Maine and her father. After seeing Atlas again, Lily accepts that Atlas remains a formative love, but Lily concludes that her current life is with Ryle, while Atlas has his own life and girlfriend.