As a Senior Inspector of the Narcotics Bureau Operation Unit, Heung Wing profoundly abhors evil. He and Wai Sai Lok, the Senior Inspector of the Intelligence Unit, have closely co-operated with each other as peer mentors, frequently solving drug trafficking cases for the Police Force. During an operation to knock down the targets, Sai Lok discovers clues that Heung Wing is most likely the corrupt cop in a collusion conspiracy with drugdealers. Apart from launching a secret investigation into Heung Wing, Sai Lok is also alienated from him by the evil-willed Chief Inspector of the Operation Unit – Pun Hok Lai. Having undergone various disputes against each other, the long-term brotherly relationship between Sai Lok and Heung Wing appears full of contradictions. On the other hand, following an investigation, Sai Lok falls in love with a snitch – Chan Ka Pik, who suffers from low self-esteem due to her humble beginning. Deliberately denying her affection to Sai Lok, Ka Pik gives up on him so that his secret admirer – Ko Hei Suen, a rookie police officer, can have the chance, leading to a subtle relationship among the three. Feeling life is so dreary, Ka Pik ultimately digs her own grave by becoming a new generation of drug dealers, involved in drug trafficking and provoking the Police Force. With intense sorrow, Sai Lok then joins forces with Heung Wing against Ka Pik, waging a chain of bitter battles.