The underworld in Massachusetts, south of Boston, is extremely rampant, and the largest gang is the Irish gang headed by Frank (Jack Nicholson). In order to eliminate them, the police decided to send police academy graduate Billy (Leonardo DiCaprio) to lurk undercover. The police officer's sarcasm made Billy, who had lived in the bottom of society, very unhappy. He once wanted to be an upright policeman, but under pressure, he had to obey orders. After the baptism of burning, killing and looting, he won Frank's trust. At the same time, Colin (Matt Damon), who is also a graduate, was rewarded by his superiors for his meritorious service in smuggling, and is preparing for marriage with his favorite girlfriend. In fact, he is a pawn planted by Frank in the police force, and the two colluded for personal gain. The police and the gangsters successively discovered the existence of an insider, and a cat-and-mouse game unfolded... This film won the 79th Academy Award for Best Picture, and Martin Scorsese won the Best Director Award.