Tian Xiaomai (played by Yang Ying) and Sheng Zan (played by Zhang Chao) have been in love for many years and are about to enter the palace of marriage hand in hand. However, at this juncture, Tian Xiaomai's father, a criminal policeman, died at work. In grief, Tian Xiaomai found a detective notebook in his father's relics, which recorded an unsolved case ten years ago, and also reminded Tian Xiaomai of his first love Qiu Shou (played by Ruan Jingtian). One day, Tian Xiaomai learned from a friend about an online store that sells everything in the world. In the store, Tian Xiaomai bought a purple scarf. After that, strange things happened one after another, and all kinds of clues showed that Qiu Shou, who is now missing, is inextricably linked to the suspicious case in his father's notebook. In this way, Tian Xiaomai investigated the case while looking for Qiu Shou, trying to find the truth hidden behind the chaos.