Zhao Xishi, who has lived for 25 years and is full of regrets about his decisions, often wishes that he could go back to his high school days, hoping that he could decide his life again, and that he could stand in front of the person he liked in high school again and get to know him again. But when everything goes back to the past, there are already different variables. The fates of Zhao Xishi, Shen Xichen, Zhou Ruoxu, and Yunran are bound together across time and space. Every butterfly effect Zhao Xishi made in the past caused earth-shaking changes in the future she returned to.