In order to solve difficult cases, the police often rely on informants to obtain intelligence. However, in the process of action, they often put informants in danger intentionally or unintentionally. A year ago, the tragic end of the informant Feihuan (played by Liao Qizhi) made Hong Kong police Li Cangdong (played by Zhang Jiahui) suffer physically and mentally. The superficial promotion could not wash away the guilt engraved in his heart. And now, he has to cooperate with new informants again. This time, he found the ill-fated gangster He Xigui (played by Nicholas Tse). In order to rescue his sister who was in dire straits, Xigui had no choice but to accept Li Cangdong's task and break into the gang of the gold robber Huatian (played by Lu Yi) to obtain intelligence. With the help of Xigui, the police have more and more evidence, and the arrest net is gradually closing. At the same time, Xigui's situation is becoming more and more dangerous. The tragedy a year ago seems to be repeated again. How should Li Cangdong choose...