Senior police officer Kang Sir was murdered. Before he died, he destroyed all the undercover information to protect these brothers who were walking on the line of life and death. After that, the police began to recover the data and reconnect with the undercovers. One day, the female undercover Ah Ding (played by Charmaine Sheh) received a code invented by Kang Sir. Under the command of her criminal police boyfriend Ah Q (played by Francis Ng), she tried to contact the mysterious undercover. On the other hand, Ah Lan (played by Nick Cheung) and Shao Zhilang (played by Louis Koo), important members of a gangster organization disguised as a legal company, jointly attacked their competitors. The two are like brothers, and they are in the limelight among the young and strong faction of the company. However, the police's prediction of their actions made Ah Lan begin to suspect that there was an insider in the company. After several attempts, Ah Ding finally contacted the mysterious undercover, but great danger also rushed towards her...