In South Boston, the state police force are waging a war on Irish-American organized crime. Undercover cop Billy Costigan is assigned to infiltrate the mob syndicate, which is run by gangland chief Frank Costello. Billy quickly gains Costello's confidence. But when it becomes clear to both the mob and the police that there are moles in their midst, Billy and the other mole are suddenly thrust into danger. Afraid of being caught and exposed to the enemy, each must race to uncover the identity of the other man in time to save himself.

Video release of a 2006 motion picture. Based on the 2002 screenplay "Wu jian dao" by Alan Mak and Felix Chong. Special features: theatrical trailer (3 min.).