Secret

In 1999, Ye Xianglun transfers into Tamkang Secondary School and joins the piano program. While exploring the famous old piano building, he is drawn to a beautiful, mysterious melody that seems to pull him toward a hidden connection. The tune leads him to Xiaoyu, a fellow piano student, marking the start of their intertwined fate.

During a campus tour, Xianglun meets Xiaoyu and spends time with her in the practice rooms and around town. Qingyi introduces him to the campus, and Xiaoyu explains that the melody is a secret that cannot be told. The encounter begins a delicate bond between Xianglun and Xiaoyu and hints of rivalry with Qingyi.

Xianglun wins a school piano battle and gifts Xiaoyu a rare music score, sparking a moment of closeness between them. They share their first kiss, deepening their romance as they navigate the school’s rhythms and secrets.

Xianglun informs Xiaoyu that the piano building will be torn down on graduation day. She reveals the mysterious tune 'Secret' and warns him not to play it on the oldest piano, implying it holds power over time. The revelation ties the building's fate to their music.

With graduation looming, Qingyi begins to get closer to Xianglun, stirring jealousy in Xiaoyu. As the triangle tightens, Xiaoyu grows increasingly withdrawn, skipping classes and retreating from the world. Tension builds between friends, lovers, and rivals.

During graduation day preparations, Qingyi lends Xianglun her bracelet for luck. Halfway through the performance, Xianglun sees Xiaoyu by the door and they share a fleeting smile before she leaves. Xiaoyu later notices Qingyi's bracelet on Xianglun's wrist, deepening the mystery.

After the ceremony, Xiaoyu is missing. Classmates recall him as always being alone, and Xiaoyu's mother reveals that she had been sick and dropped out long ago. Xianglun's search widens from the campus to Xiaoyu's home as he seeks answers.

Xianglun's father confronts Xiaoyu's tale, which unfolds as Xiaoyu describes 1979 when she spoke with the teacher and found the score 'Secret'. By playing it on the oldest piano, she traveled 20 years into the future. She explains her constraint: she can only be seen by the first person she sees, explaining her sporadic disappearances.

Xiaoyu's story is relayed to the classroom and Xiaoyu's mother, causing whispers among the 1979 cohorts. The legend of time travel takes root, creating a haunting link between Xianglun's present and Xiaoyu's past.

Back in the present, Xianglun realizes the score 'Secret' is the key to time travel and could move him through time if played at the right speed on the old piano. He hurries toward the piano building as the demolition accelerates.

Xianglun's father retrieves Xiaoyu's manuscript, which contains a message to Xianglun from twenty years earlier. The back-of-page note corroborates Xiaoyu's account and deepens the mystery of time travel.

In the piano room, Xianglun plays 'Secret' from memory, following Xiaoyu's instruction to play fast to travel back. The demolition crashes around him as he completes the last note, leaving his fate implied but hopeful.

Outside the classroom, Xiaoyu looks in and smiles at Xianglun, a quiet acknowledgment of their bond across time. The film closes with a 1979 graduation photo showing Xianglun and Xiaoyu standing together in the same frame.