Early in Gone Baby Gone, protagonist Patrick Kenzie (Casey Affleck) ominously muses, “When I was young, I asked my priest how you could get to heaven and still protect yourself from all the evil in the world. He told me what God said to his children: We are sheep among wolves. Be wise as serpents, yet innocent as doves.”

Set in the gritty Boston neighborhood of Dorchester, Gone Baby Gone begins with a hunt for a missing four-year-old, Amanda McCready (Madeline O’Brien). Helene McCready (Amy Ryan) seems like a pathetic waste as her mother, but Amanda’s Uncle Lionel (Titus Welliver) and Aunt Bea (Amy Madigan) are determined to pull out all stops to find the girl. They hire a team of young private investigators, Patrick Kenzie and Angie Gennaro (Michelle Monaghan), mostly because they are neighbors who presumably can navigate routes in Dorchester that are closed to cops.

At first Angie and Patrick are stymied, but once they join forces with hard-boiled (as in steel-plated) detective Remy Bressant (Ed Harris) and obsessed but avuncular police captain Jack Doyle (Morgan Freeman), they begin to make progress.

The twists and turns that fill the world of Boston hustlers, dopers and criminals involve a good deal of danger for Patrick and Angie, who are not nearly as naïve as they look. Other people may be using them for their own ends, but the young lovers have a way of surviving the jungle in a way that bodes well for their future, not that they don’t suffer their share of setbacks and defeats. They are a Nick and Nora Charles for the 21st century, navigating a working man’s world with wit and compassion.

One of the triumphs of Ben Affleck and Aaron Stockard’s screenplay is that while it looks gritty violence straight in the eye, it never celebrates crime. All of the characters in the film have added dimensions—usually flaws—not apparent at first glance. This also holds true of Patrick and Angie. One has the feeling that if Gone Baby Gone were twice as long, we would see even more surprises from people we thought we already knew.

Under Ben Affleck’s guidance, his younger brother Casey gives a breakthrough performance, but there are many exemplary turns here: Ryan as a dope-addicted manipulator as willful as a pit bull; Freeman as an even-keeled philosopher-police captain; Harris as a warmhearted rogue cop; Monaghan as a woman with a good head on her shoulders and the strength to follow her own convictions.

Production values are as strong as the casting. Cinematographer John Toll catches the tired look of fading bars and the mean décor of people who, try as they might, can barely muster the bucks for a decent kitchen chair. Sharon Seymour’s production design is surprisingly versatile, capturing city precincts, urban and rustic exteriors as well as criminal abodes with a slightly menacing authenticity.

For all the rough-and-tumble action sequences, skillfully choreographed by Affleck, Gone Baby Gone is a thinking man’s crime film, whose deeply etched characters and brilliant plotting have a near-Shakespearean power. The conclusion of the film seems simple, quite banal, but achieves considerable power without the need for kettledrums on the soundtrack