Hua Long, Su Mei, Bao Zhan and Professor Liang comprise the SIG (Special Investigation Group). This group deals with the extremely abnormal and twisted investigations of homicide cases that are difficult to crack. In the process of solving the cases, each member must face their own dangers, conspiracy and growth.

• Hans Zhang
• Eric Tsang Chi-Wai
• Jim Yu
• Zhang Yamei
• Dai Tingrui
• Zhang Haocheng
• Sun Shuang
• Fu Jun