Police Detective Don Lee (Nick Leung) makes a bad call, causing a close informant to be injured. A year later, he must locate a new man to go undercover inside a jewel-theft ring. Ghost, Jr. (Nicholas Tse) doesn't want to do it, but Lee can offer deals and apply pressure that makes it hard to say no.
Lee makes decisions based on the progress of his case, but not always at the benefit of his informant. Ghost must play a role, but can't decline the chance to do what's right.