Actor Casey Affleck is earning critical raves for his portrayal of an inexperienced Boston private investigator in a gritty new film mystery that marks the directing debut of his older brother, screen star Ben Affleck. The drama about a missing child is adapted from a best-seller by novelist Dennis Lehane. Alan Silverman has a look at Gone Baby Gone.

A little girl named Amanda has disappeared from her home in Dorchester, a working class neighborhood of South Boston. Frustrated by and, perhaps, not trusting the police, Amanda's family turns to Patrick Kenzie, a young private eye who grew up in their community.

As Patrick gets deeper into the case, he finds a twisted web of crime and corruption that must be swept away in order to find the little girl; and he also finds his morals and ethics put to the test.

Ben Affleck on the set of Gone Baby Gone

First-time director Ben Affleck, who shared a screenwriting Oscar with Matt Damon a decade ago for Good Will Hunting, co-wrote the script for Gone Baby Gone. Affleck says he was drawn to the themes in the Dennis Lehane novel, but made some significant changes when he decided to direct the film version.

"When I first read the story I thought I was going to develop for myself to act in," Affleck explains. "Then I wrote the script and got to a place where I didn't want to act in it if I was going to direct it. Then I couldn't really think of an actor (aged) 35 - 40 that was right and that I could get. Also, I didn't really like it that age. I thought it would be much better if I made it 29 or 30 because I thought the character would have more distance to travel. You know, if you're 40 and something bad happens to you, you are kind of scarred, but it doesn't change who you are going to become ...it doesn't 'fork the road' of your life. I thought 'maybe I'll make him 29 or 30 ...I can get this actor who is like an amazing actor who is from Boston who I can get and afford.' It all came together for me."

That actor is his younger brother, Casey Affleck.

Casey says Patrick may display the bravado of a typical movie P.I., but the goal was to make him much more like the real thing.

Casey Affleck in scene from Gone Baby Gone

"There is the cinematic idea of the private investigator we've seen a million times: the guy smoking in the shadows, trailing people and stakeouts and shoot-outs ...that sort of thing. It's sexy and kind of glamorous and a little tough; but this wasn't that because in our experience that doesn't really exist," he says. "A lot of these private investigators spend most of their time at a desk gathering information on the Internet and sending information out on the Internet. They do a certain amount of 'field work,' but it's more mundane, kind of workaday and doesn't pay a lot. That's what we wanted to show and I liked that part of it because it made the rest of the movie work for me. He's somebody who hasn't experienced some of those gray areas of morality."

Michelle Monaghan plays Patrick's partner, Angie Gennaro.

Casey Affleck and Michelle Monaghan in scene from Gone Baby Gone

"What I loved about this movie is here you have this very independent woman who is doing a job that is non-traditional for a woman," she explains. "That really appealed to me; and it wasn't necessarily a romance. They were a team, professionally and personally, and I like the idea that they have this sort of equitable relationship."

Much of the moral dilemma revolves around the missing child's mother: a drug addict whose irresponsible behavior may have led to the disappearance. She's played by stage veteran Amy Ryan who says she tried to find the character's humanity.

Amy Ryan in scene from Gone Baby Gone

"I suppose by just having compassion (for) what seems on the page to be such a dark, evil character. If you start with compassion and say 'why is she in this situation?' Okay, she doesn't have a husband ...child care ...education ...any social structure holding her up. I don't condone it, but no wonder she fell into some of the choices of drugs and alcohol. It's probably the pattern of her family before. It's the cycle," Ryan says.

Gone Baby Gone was filmed on the streets of South Boston with many local residents as background players. The cast also features Morgan Freeman as a police captain haunted by his personal experience with a child abduction; and Ed Harris plays the jaded but determined police detective trying to solve this latest case. The screenplay is co-written by Aaron Stockard and director Ben Affleck.