Hong Kong action thriller directed by Ringo Lam. When an undercover police officer investigating a gang of jewel thieves is killed, officer Ko Chow (Chow Yun-fat) is instructed to continue his work. Soon he is fighting battles on multiple fronts with his boss wanting him to infiltrate the gang, his girlfriend threatening to leave him if he will not marry her immediately and a newly-formed police task force who do not realise he is one of them tracking his every move.

Meanwhile, as he bonds with Fu (Danny Lee), one of the thieves, he struggles with the thought of betraying him. When their next heist goes wrong, the gang fear there is a traitor in their midst and as the police close in, will Ko survive the ensuing confrontation?