In the 37th year of the Wanli reign of the Ming Dynasty, a series of murders occurred in the county town of Yuxian, Jiangnan. The identities of the deceased were different and unrelated to each other. The bodies were arranged in strange postures, and a message was left at each crime scene. As the apprentice of the first victim, the young detective Qu Sangeng worked with his friends to investigate. As the investigation deepened, people from all walks of life, including scholars, farmers, merchants and businessmen, appeared one after another. In the fog, an old case from 20 years ago surfaced. Who is the murderer and what is his purpose?