“I always believed it was the things you don’t choose that make you who you are: your city, your neighborhood, your family.”

Patrick Kenzie, the main character in Dennis Lehane’s Boston-based detective series, forms this observation in the opening credits of the latest film to be made of the novels, Gone Baby Gone (the first was Mystic River). The voice-over plays as the camera pans through a working class neighborhood of burly, rough people in a surly, rough place. And while on one level Kenzie’s observation on choice as constitutive of essence can be conceded, it takes the entire movie before its deeper levels register. Because while it’s true that much of what we are is not of our choosing, it’s truer still that a greater part of our identity lies in what we’ve resisted doing.

In other words, as revealing of our real selves as our positive choices may be, just as telling are those things we’ve left undone: our choices “not to.” Perhaps therein lies a double virtue: in every choice to do the right thing, there is another not to do the wrong.

Ben Affleck and Aaron Stockard adapted the screenplay from the Lehane novel, and the film stars Casey Affleck as Kenzie and Michelle Monaghan as his colleague and lover, Angela Gennaro. The plot revolves around the abduction of a four year-old girl, the daughter of cracked-out barfly, Helene, who has embraced with relish all of the foulness of her surroundings (Amy Ryan, in a wonder-inspiring performance).

After Helene’s brother and his wife approach the detectives about supplementing the official investigation, Kenzie and Gennaro meet with resistance from both Helene and the police. But what keeps the movie from sliding into a predictable race of “hard-nosed gumshoe vs. bumble-prone cops” is a plot twist that makes the film a profound example of a moral dilemma.

The detective in charge of the missing children’s unit (Morgan Freeman) had lost his own daughter in an abduction/murder years back, and one of the cops assigned as liaison to the detective pair (Ed Harris) has been involved in similar child-rescues in the past. Worse still, blame for the girl’s kidnapping is partly due to Helene’s job as a mule for a drug lord. Fear for her own safety, along with a native viciousness, overwhelms Helene, which makes her hard to forgive even when a genuine sorrow erupts through her callousness.

Questions begin to stack up on odd sides. Instead of a distraught, bereft mother as the sympathetic character, others in the film seem to care more for the child’s recovery than she. Finally, the possibility of peculiar motives behind the girl’s disappearance play out amidst a sick, soiled backcloth of existence in which small children are traumatized by rapacious creatures it is hard to call human.

In such a place, with such people, what is doing the right thing by the child? What measures should be taken to rescue her, and from whom should she be rescued? In what life and place lie the components of promise and hope, far from the blueprint for doom that seems her fate? She has chosen none of this; it has chosen her.

On the other hand, there are things that can be done about the situation, and things that can be refused. Not all measures, however good they seem, can be taken up. Kenzie’s priest-guided conscience conducts him through this murky terrain. And while everyone seems to want what’s best for the girl, only Kenzie makes a promise to Helene. He will not achieve the good for the lost child by denying her mother’s stake in it. He alone will not presume to say what the best thing is, or deign to allot the roles of those who can have a part in bringing it about.

Here the hero acknowledges primal bonds that defy sociological theory. But the honesty of the film refuses to reward his hard decisions with a candy cane finish. He must live with both the things he has chosen, and more importantly, the things he could not bring himself to do.

In the end, one uncomfortable truth rings loudest: the good—however devoutly wished for—cannot be stolen.