With his directorial debut, "Gone Baby Gone," Ben Affleck proves he belongs behind the camera instead of in front of it. Based on Dennis Lehane's novel of the same name, Affleck deftly constructs a gritty look at life on the wrong side of the tracks and how that lifestyle can blur the borders of right and wrong.

The story begins after local news stations pounce on the story of Amanda McCready (Madeline O'Brien), a missing 4-year-old girl who lived in a run-down part of Boston with her crack-addicted mother. Amanda's aunt distrusts the police's ability to find her niece, and she and her husband hire a private detective, Patrick Kenzie (Casey Affleck, "Ocean's Thirteen"), who grew up in the neighborhood and has ways of getting information unavailable to the law officials.

The captain of the case, Jack Doyle (Morgan Freeman, "Million Dollar Baby") and his two top detectives, Remy Bressant (Ed Harris, "A History of Violence") and Nick Poole (John Ashton, "Beverly Hills Cop") distrust the young PI, going so far as to suggest Patrick go home and read a Harry Potter novel. But soon enough, it becomes clear that although Patrick may be in over his head, he does have a few tricks up his sleeve.

Like any great mystery movie, things are not always as clear as they seem. In a way, that is what "Gone" is really about. In today's world, acts and ideas that should be clearly right or wrong can often be muddled by the reality of life.

Unlike many flashy and hollow Hollywood films that reveal all their cards in a preview months before they open, "Gone" keeps the audience guessing until the end. And when it is all said and done and the credits are rolling, there is still no obvious answer to the questions the film raises. Instead, each audience member must put him or herself into the film's final moments and ask what they would do if put to the same test.

 Casey Affleck, who is coming off a critically acclaimed performance in "The Assassination of Jesse James by the Coward Robert Ford," proves he is up to the task of leading an all-star cast. Despite his slight frame and boyish face, Casey is able to play Patrick as a tough guy who slowly realizes he is not be as smart as he once thought.

As usual, Freeman and Harris are amazing, adding depth and nuance to characters which, if handled by lesser actors, could have turned into caricatures. But Amy Ryan's performance as Amanda's drug-running mother should be noticed during award season. Ryan goes all out, putting all of herself into "Gone's" most provocative character.

With the help of their supporting cast, the Affleck brothers turn in career-best work on "Gone," a film about big ideas of morality disguised as a cops and bad guys mystery. It is a must see for anyone looking for a thought-provoking movie.

"Gone Baby Gone" is rated R for violence, drug content and pervasive language.