Martin Scorsese directs an all-star cast in this action-packed thriller set in Boston, where a long-simmering hostility between the police department and an Irish-American gang led by Costello (Academy Award winner Jack Nicholson) is primed to explode. The fuse is lit when a gangster (Matt Damon) is chosen to infiltrate the police force and a young cop (Leonardo DiCaprio) goes undercover within the gang. Now, when the two moles uncover each other's identity, the battle begins._