A drug cartel boss is arrested in a raid and coerced into betraying his former accomplices as part of an undercover operation.

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).

To take down South Boston's Irish Mafia, the police send in one of their own to infiltrate the underworld, not realizing the syndicate has done likewise. While an undercover cop curries favor with the mob kingpin, a career criminal rises through the police ranks. But both sides soon discover there's a mole among them.