A high school student, Ye Xiang Lun (Jay Chou) transfers to Tamkang High School, a school famous for its students' performance in playing piano. On the first day of school, while wandering through the piano building, he hears an unknown and alluring melody played by a fellow female student, Lu Xian Yu (Kwai Lun-Mei). Thereafter, Xiang Lun and Xiao Yu falls in love. As Xiang Lun seeks to know more about the melody Xiao Yu has played earlier, she tells him that it is a secret that cannot be told. Later on, a misunderstanding transpires, and Xiao Yu mistakenly thinks Xiang Lun is cheating on her with another girl, Qing Yi (Alice Tzeng). Xiao Yu then vanishes from Xiang Lun's world without leaving a trace. Five months later, Xiang Lun plays "Le Cygne" in tribute to Xiao Yu in their school's graduation ceremony. Xiao Yu unexpectedly reappears, looking sad and languid, and vanishes again. Xiang Lun later realizes that her existence is known to only he himself. In the pursuit of Xiao Yu, Xiang Lun finds an old photo depicting both his father (Anthony Wong Chau Sang) and Xiao Yu. From his father, Xiang Lun finds out about Xiao Yu's past. As all the pieces fit in, Xiang Lun finally realizes that Xiao Yu had come from the past, and that the melody played by Xiao Yu is the method by which she traveled through time. Xiang Lun cycles back to his school and sneaks into the piano building, which is being demolished as he does so. He plays the melody, finishing barely before the final destruction of the building. He travels back in time, and is reunited with Xiao Yu. The story ends with both Xiang Lun and Xiao Yu adjusting each other's attire as they prepare to take their graduation photo.