Chan Wing Yan, a young police officer, has been sent undercover as a mole in the local mafia. Lau Kin Ming, a young mafia member, infiltrates the police force. Years later, their older counterparts, Chen Wing Yan and Inspector Lau Kin Ming, respectively, race against time to expose the mole within their midst.

Five police officers in Hong Kong are kidnapped. The police commissioner is on a business trip overseas. Two vice commissioners, Sean Rau and M.B. Lee, then take over the case. The two vice commissioners are rivals who both vie for the police commissioner seat. At first, M.B. Lee takes the lead in the case, but comes to a dead end. Sean Lau then takes the lead, but he falls into a trap. Both men are then investigated by the ICAC (Independent Commission Against Corruption).