After the death of her policeman father, Xiaomai () begins to look over his old journals filled with notes about the cases he investigated over the years. The mention of a purple scarf in the notes particularly catches her attention, prompting her to purchase a similar scarf from a mysterious website that claims to sell everything, as long as one can pay the price. Soon after, Xiaomai's close friend () is found dead, strangled by a purple scarf. All of this awakens Xiaomai's memories of her childhood sweetheart Qiushou (), whose mother was also strangled to death with a purple scarf by an unknown killer. Xiaomai and Qiushou grew up together and fell in love, but he suddenly disappeared from her life 15 years ago without a word. She begins to believe that Qiushou has returned and may be seeking revenge.