A woman's body is discovered in a river near Qunyi Village in Kuncheng. Detective Captain Sun Weiwu takes charge of the investigation. A forensic autopsy reveals that the victim had been sexually assaulted before her death, and his girlfriend, Gu Fan, uses the traces at the scene to deduce that she was murdered. Just as Sun Weiwu organizes the police to investigate, two more murders occur in quick succession. Based on the distinctive features of the crime scenes, the police soon link the cases together.
After a series of investigations, the police identify the suspect as Chen Dafa, the head of Qunyi Village. But just as they prepare to arrest him, they discover that he has been murdered inside a locked office. The police cannot make sense of the killer's method, so Sun Weiwu has no choice but to seek help from his girlfriend Gu Fan and her powers of deduction. With Gu Fan's meticulous logic, the whole case is finally unraveled, piece by piece~~