Ted Demme's Monument Ave. is a tense look at the mean streets of Boston and the mob-like politics of its Irish-American car theft racket. Looking comfortable in his native environment, Denis Leary makes his most convincing case yet that he is truly an actor, rather than just a standup comic trying to pass as one. Excelling in the role of the conflicted thief who serves as the film's moral center, Leary leads an all-star cast focused more on their performances than on trying to manufacture Boston accents. There's nary a false note in the process. While Monument Ave. doesn't exactly cover new territory, it does contain interesting insight into the winking relationship between the police and the hoodlums in such an insular neighborhood. When the character played by Billy Crudup, who shines brightly in a brief appearance, gets whacked, the lead investigator (Martin Sheen) goes about his rote interrogation of the witnesses, knowing full well each will claim to have been in the bathroom when the shots rang out. Sheen's ethics end up proving almost as blurred in an environment where everybody knows the secrets, but never voices them. The dynamics of this familial community are forever intriguing -- by night they test each other in terrible ways, but by day they still gather for games of street hockey. Although generally downbeat, the film is relieved by some funny sequences in which the actors get to revel in Mike Armstrong's talky screenplay.