The undercover cop Chan Kam-wah, investigating a group of jewellery thieves, blows his cover and is stabbed to death by three attackers in a public marketplace. His superior, Inspector Lau, orders Ko Chow, another undercover policeman, to resume the investigations. Ko Chow accepts reluctantly: he would prefer not to perform another undercover assignment, since he had to arrest someone during his last mission who had trusted him as a friend.