Because of a fatal shooting case, plain-clothes Sergeant Ko Lik-kei (Him Law) runs into a "dull" and "troublesome" witness called Lee Ho-fan (Willie Wai). Lik-kei is instructed to protect Ho-fan at all times. Initially, the duo are strangers that cannot stand each other. They then gradually get along. Meanwhile, an apparel company of which Ho-fan is a major shareholder is found to have involved in illicit dealings. Yip Cheung-lok (Lau Kong) and his son Yip Ming-kwan (Tsui Wing), who are member of senior management, are associated with these activities. Lik-kei teams up with Ho-fan and Ho-fan's younger sister Lee Chung-ying (Kelly Cheung), who is a barrister by profession, to investigate. Lik-kei and Chung-ying get entangled in a relationship in the process. Also, Lik-kei's elder sister Ko Wing-yum (Pinky Cheung) and Ho-fan get along sometimes and provoke each other at other times. Fate has brought the foursome together, causing a case that has remained unsolved for more than twenty years to be reopened.