Lin Beixing, an "experienced girl" who is about to enter her 30s, missed out on achieving her dream of love as her boyfriend, Zhan Yu, breaks the contract, and her life and work have become a mess. However, not sure if this is the God playing tricks on her, Lin Beixing returned to the age of eighteen. The third year of high school is a nightmare, but Lin Beixing decided to retake the college entrance examination and get rid of Zhanyu, to live anew for herself. However, Lin Beixing's sweet dream was dashed by a boy called Zhang Wansen. The accidental encounter of Zhang Wansen after the college entrance examination became the switch to end Lin Beixing's time and space journey. Lin Beixing began to investigate the cause of Zhang Wansen's death and embarked on a difficult journey to save Zhang Wansen. The days in high school were romantic and short, and Lin Beixing's changes allowed her to reap the beautiful moments that she had neglected. With the arrival of summer, Lin Beixing also found that she not only saved Zhang Wansen, but also saved the boy's love for her since she was young that is deeper than the sea....