The criminal police headed by He Bu from the Jingcheng City Public Security Bureau have been investigating the drug trafficking case of the Yue Cheng gang. Due to insufficient evidence, they have been unable to start. One day, He Bu happened to encounter Yue Cheng suspected of murder and brought him back to the police station. The murderer killed Luo Xiaolan because he wanted to get back a priceless diamond necklace that was engraved with the password of all the criminal evidence and financial status of the Yuecheng Group. After Luo Xiaolan died, only Luo Xiaomei knew where the necklace was hidden. The police hope to prosecute Yue Cheng for intentional homicide, and search for evidence of his drug trafficking and other cases, so as to wipe out his drug trafficking organization. For her own greed, Luo Xiaomei did not cooperate with the police at first, which brought the case investigation to a deadlock.