Wraith spirits kill people. Xia He, a girl from the underworld, takes her good friend Xiao Zhi to the school in the middle of the night to look for Momo, a girl who may become a wraith spirit due to suicide, hoping to prevent her from killing people again. In the classroom, they meet Jun Zigan, a night watchman in the world. They don't know each other before they fight. The three of them work together to prevent the revenge of the wraith spirits. Unexpectedly, things are complicated and Momo is not the murderer. Who is?