Li Yuyu's biography Sun Qingqing has provided clues to solve the case. After the scene, the fierce murderer wanted to kill Sun Qingqing, but Zhang Yi, who had been ambushed for a long time, was on the spot. Behind the scenes, the murder of the net was confessed. His purpose was to destroy Sun Qingqing’s marriage. The schooler received a threatening letter and his son suffered from a strange disease. Five years ago, a plague occurred in the city. In order to block the slaughter of the affected area, the relatives of the patient murdered the son of the school for revenge. Li Yuyu dressed as a woman sneaked into the Taishou House and found out the list of plague patients. The identity of the murderer finally surfaced.