Say the name Ben Affleck, and myriad images come to mind.

The loyal Red Sox rooter and John Kerry campaigner. Half of the Oscar-winning Matt-and-Ben "Good Will Hunting" duo. Another half of the tabloid-fodder "Bennifer" couple. A sometimes-solid actor ("Hollywoodland," "Boiler Room") prone to weak movie choices ("Bounce," "Daredevil," "Gigli").

"Gone Baby Gone" will leave you with a new picture: filmmaker.

In his directing debut, Affleck has found his calling. Co-writing the script with longtime friend Aaron Stockard, Affleck presents a place oozing with atmosphere and rich, complicated characters. He has enough confidence in himself (and in us) never to go for the safe, easy answer.

"Gone Baby Gone" is set on the rough streets south of Boston. Much has been written about Affleck's decision to populate the background of this gritty crime drama with authentic locals; he even gave several of them speaking parts during crucial scenes in run-down bars. It was a bold move that paid off big-time. You feel as if you've been immersed in an insular neighborhood, where your block is your entire world and secrecy is a critical trait.

Private investigators Patrick Kenzie (Casey Affleck, Ben's younger brother) and Angie Genarro (Michelle Monaghan), partners in work and love, are hired by the family of the abducted 4-year-old girl Amanda McCready. The relatives figure that no one in the neighborhood wants to tell police if they saw or heard something, but they'll talk to a local guy they know and trust.

Patrick and Angie persuade the chief of the Crimes Against Children department (Morgan Freeman, among the superb supporting cast) to let them tag along with the detectives assigned to the case. Remy Bressant (a powerful, unpredictable Ed Harris) and his partner, Nick Poole (John Ashton), grudgingly agree to meet and talk with them, but Patrick suspects from the start that they're not being entirely forthcoming.

This is a hunch that will hold true for nearly every single character in "Gone Baby Gone," including Amanda's mother, Helene, a difficult role masterfully portrayed by Amy Ryan. Helene is an alcoholic, junkie, sometime-prostitute and drug mule. She probably loves her daughter but is so screwed up and selfish, she's also unapologetically neglectful.

Just when you think Patrick and Angie have solved the case, another wrinkle emerges — then another and another. Affleck keeps you hanging on, wondering where he's going next. And the younger Affleck serves as an engaging figure to help us navigate the story's many turns. He comes off as a regular guy who can be both forceful and frightened, and his character ultimately faces decisions that would trouble anyone.

That pervasive sense of moral ambiguity is one of the strongest elements of "Gone Baby Gone," and it will you keep you thinking and talking about the film long after it's over. This much is indisputable, though: Ben Affleck is a director who surely has more great things in store.