Inspector Q (Francis Ng) and agent Ding Siu-ka (Charmaine Sheh) are top members of CIB Department, they are after a drug racket that is taking over the city. Unexpectedly, they receive a mystery message from a missing undercover agent "Blackjack". CIB tries to locate and process Blackjack before it's too late. The paranoid drug mafia leader Tung Pak-ho (Li Guangjie) plays his own troop on each other's throats, suspecting a mole. Meanwhile, boss Blue (Nick Cheung) and his right-hand man Shiu Chi-long (Louis Koo) participate in an internal struggle to become the top dogs irrespective of their strong friendship.

After surviving and shooting their way out of a drug deal ambush in Brazil, Rio de Janeiro, it becomes clear that Blue is Blackjack and upon knowing this, Shiu Chi-long tries to protect himself by using Blackjack's identity. They survive doubts and struggles between them but only for Blue to lose his life to an assassin sent by ruthless Tung Pak-ho. Inspector Q's life is lost facing goons and Ding's life is saved by her godfather Foon Hei Gor (Hui Shiu-hung), who is an undercover agent posing as a legendary retired don who is looking to get back into the criminal underworld in the city. Finally, Foon Hei Gor gets Tung Pak-ho arrested after punishing him for what he had done to his wife when Tung Pak-ho started out as a criminal.