During the Wu and Zhou Dynasties two young girls from from different classes - Zhao Qingqing, the daughter of the captain of the Jingwu Guard, and Xiao Li, a girl from the lower class of the city - were accidentally involved in an unsolved case

The film is adapted from the novel of the same name written by Yan Zhiyang. It tells the story of Shen Tuo (Liu Lincheng), a descendant of Mohist's official technique, who enters the Promise Prison alone in order to rescue his beloved wife, Jiang Ren (Liu Jingyi).