In a shooting case, plainclothes Sergeant Ko Lik-kei (Him Law) meets the "dumb" and "troublesome" eyewitness Lee Ho-fan (Wai Ka-hung). Lik-kei is assigned to protect Ho-fan, and the two gradually accept each other from being strangers and resisting each other. At this time, the garment company of which Ho-fan is the majority shareholder is found to be involved in criminal transactions, and the company's senior executives Yip Cheung-lok (Lau Kong) and Yip Ming-kwan (Tsui Wing) and his son are involved. Lik-kei joins forces with Ho-fan and his sister Lee Chung-ying (Helen Cheung), who is a barrister, to investigate. During this period, Lik-kei and Chung-ying develop an entangled relationship, and Lik-kei's sister Ko Wing-yin (Princess Cheung) also becomes a grudge against Ho-fan. Fate brings the four together, and a cold case from more than 20 years ago is reopened...