Affleck has returned to his old Boston stomping ground to film a novel by Dennis Lehane, the East Coast James Ellroy whose writings previously inspired Mystic River. It's here we find Patrick Kenzie (Casey Affleck, the director's younger brother) and Angie (Michelle Monaghan), a pair of lovebird private investigators hired by the family of missing four-year-old Amanda McCready, specifically for their local knowledge and contacts. The idea is that while the cops, as represented by Morgan Freeman's captain, trawl the city's surface for leads with which to assuage the hysterical news media covering the case, the investigators - in conjunction with a pair of hardened detectives (Ed Harris and John Ashton) - can focus on the underbelly of the case, arranging meetings with various lowlifes, pederasts and drugrunners who might have crucial beans to spill, but wouldn't dream of going to the authorities.
One twist is that the girl's mother Helene (Amy Ryan) could hardly, herself, be any less of a saint. Her house a mess of half-eaten food and unwashed plates, she sits on her sofa watching Wife Swap and Springer, while the investigators uncover sorry stories of parental neglect - how Helene took her daughter to a bar while she was dealing drugs, for example - that don't, ultimately, make Amanda's disappearance any less regrettable or haunting. It's in this way that Gone Baby Gone evokes a working-class locale in a fashion that goes beyond Good Will Hunting and Mystic River both. The dialogue Affleck and co-writer Aaron Stockard have inherited from Lehane has a genuine, credible saltiness, their material shading over into genuinely disturbing territory in the depiction of a paedophile ring known as "The Addams Family". Throughout, we see how a lack of money can very easily equate to a lack of protection and proper care for our children; the view is altogether chilling.
It's a good thing we have a good guy for a hero. Affleck Jr., the best thing about the otherwise long-winded The Assassination of Jesse James..., is a flinty, scrappy presence in an Irish-green tracksuit top, and the film gets some mileage from the fact the man assigned with tracking this little girl down rather resembles a pipsqueak barely out of short pants himself. ("He just looks young," Angie insists, as her partner attempts to talk tough in a bar.) Films directed by actors tend to be more generous than most towards their performers, but this is one of those rare occasions where everyone from the top-billed players to the kids on bikes who shout one line of abuse at the passing Affleck's car ("Go fuck your mother") feels absolutely right for their part.
Ryan got the Oscar nomination, I suspect in part for keeping a character who otherwise might have come to resemble My Name is Earl's Joy from becoming a total joke, but also for convincing us, in certain scenes, that Helene deserves a second chance. There's yet more outstanding work from Harris - here fiercely, hilariously sardonic - and his real-life wife Amy Madigan, blanched and drawn and tutting memorably away on the sidelines as the missing girl's grandmother. Affleck allows us to rediscover some actors (it's good to see Beverly Hills Cop's doughty John Ashton back as Harris's partner) and offers others the possibility of a renewal. He's the first director in a while to get anything beyond nobility out of Freeman, and first ever to get more from Monaghan than pretty simpering: the actress turns a putative eye-candy role into the tough, smart cookie Angie needed to be, and only breaks down in tears at a point in the narrative when anyone with any semblance of maternal instinct - with any hope of being a good parent - would.
These actors remind us this is a thriller about people first of all, and what happens when circumstances lead us to fear the worst. As Angie puts it: "I don't want to find a little kid in the dumpster... I don't want to find a little kid after she's been abused for three days." (Events will spare her, if not us.) Affleck, an at best variable actor, has displayed commendable sensitivity in delaying the film, but its release reveals him to be a director of immense skill. The delay confers upon Gone Baby Gone true distinction: for when was the last time a dark, intelligent, involving picture such as this was released in British cinemas during the summer months? Or indeed a film that appears motivated by a deep wellcore of human sadness, by a weary acknowledgement - one you wouldn't necessarily have to be a McCann to share - that this world isn't quite as perfect as we might want it to be?
Gone Baby Gone screens on BBC1 this Wednesday at 11.15pm.