A successful serious crime investigation police unit, headed by articulate senior detective Chan (Simon Yam), tackles crime with three other detectives from different backgrounds. Martial arts expert Ma (Donnie Yen) is set to take over as head of the unit, replacing Chan who wants to have an early retirement. Ma is determined to put things right. Po (Sammo Hung), an upcoming figure in the underworld with interests in every kind of criminal activity, and Jack (Jing Wu) – Po’s right-hand man, is a reclusive cold-blooded killer.