One year after the diary first became part of the display at Amsterdam’s Anne Frank House, the protective glass over the first volume shatters. As ink from a fountain pen pools on the pages, the words lift off and take form as Kitty, a bright‑haired 14-year-old who had been Anne’s imaginary friend while she wrote. Inside the museum, Kitty quickly realizes she is invisible and untouchable to the living, watching civilians drift through the rooms and glimpse history from a distance. The scenes flash back to Anne writing, and Kitty remembers those moments as if Anne herself were speaking through the diary.
After night falls, two drunk men hurl rocks at Anne’s bedroom window once they notice Kitty turning on a light, drawing the attention of the police and forcing Kitty to flee with the diary in hand. With no clear place in the world outside the diary, Kitty tries to file a missing‑person report, but the officers are bemused and redirect her to different spots around Amsterdam named after Anne Frank before they decide to arrest her when they learn she possesses the diary.
Kitty escapes and meets a boy named Peter, whom she had seen the day before in the Anne Frank House, initially mistaking him for Anne’s boyfriend. While they skate together, Kitty learns that venturing too far from the diary will dissolve her into ink. Peter leads her back to the Anne Frank House the following morning after Kitty nearly dies from separation from the diary, and after a day of rest, Peter returns, drawing the police’s ire for their disruptions. They interrogate him about Kitty but refuse to believe his account of a magical companion.
That night, Peter explains how Kitty’s powers work, and the two of them slip away again when the authorities close in. The next morning, Kitty bars herself in by trading one of Auguste van Daan's hidden watches for modern clothes and visits the library at a Montessori school to catch up on history. After paging through several editions of Anne’s diary, Kitty learns more about Anne’s fate from a librarian who gives her Otto Frank’s book before she attends a play about Anne herself. When she criticizes the performers for misquoting Anne, the audience recognizes her from the news and crowds around, forcing her to flee once more.
In a shelter where refugees gather, a girl named Awa explains their plight and shows Kitty how her father plans to build a hot air balloon to help them escape. Kitty confronts [Peter] about his inability to tell her that Anne and most of her family did not survive, and she resolves to retrace Anne’s steps. Their journey takes them by train to Westerbork, Auschwitz, and Bergen‑Belsen, where Kitty reads Otto Frank’s memoir and views recordings of Hanneli Goslar, sinking further into despair as the scale of loss becomes painfully real. Arriving at Anne and Margot’s cenotaph in Bergen‑Belsen, Kitty collapses in sorrow, but Peter convinces her to return to Amsterdam together.
Back in the city, a government plan to deport the refugees looms the next day. Armed with new resolve, Kitty uses her experiences to empower the people around her, even spray‑painting the hot air balloon to reveal its location to the world. A crowd gathers as she delivers an impassioned speech, condemning the tendency to pedestalize Anne and urging concrete action to shelter those in need. When fear deepens, Peter offers to take Kitty back to the Anne Frank House to live as an immortal, invisible spirit, but she declines, because they have fallen in love.
With officials finally listening, the diary is handed to Awa, who delivers it to the authorities, and Kitty walks away with Peter. After a brief moment apart from the diary, she and Peter share a heartfelt kiss before Kitty dissolves into ink and disperses with the wind, leaving behind a message that continues to ripple through history.
