Kwai (Wong Hei) became an undercover after he left cadet school. Through the course of his investigaton, he got to know the Malaysian actress Kum (Fu Ming Hin) and Pok (Ngai Chun Kit), one of the member of the Witness Protection Unit (WPU). After Kwai accomplished his mission, he was transferred to the WPU to work with Pok. They made perfect partners and were appointed to protect Wah (Cheung Kwok Keung). Wah was in fact a deadly criminal in disguise. When Kwai discovered that, Wah immediately took action to ruin him. Fortunately, with the help of Pok and Wah's sister, Gi (Tong Po Yu), Kwai eventually succeeded to arrest Wah.