The Messenger (15)

Starring: Ben Foster, Woody Harrelson, Steve Buscemi

Death turns up at the front door in The Messenger, an exceptional and harrowing drama about the Iraq war that never strays outside the suburbs of New Jersey. Its centrepiece is a scene, reprised six times in slightly different ways. Two soldiers in severely smart military rig knock at the door of a house and, in tones of grave sympathy, tell the answering parent, or spouse, that their loved one has just been killed on active duty. The reaction to this appalling news is generally one of convulsive shock, but in the course of the film we also register accompanying degrees of rage, violence, disbelief, breakdown. The next of kin know what the arrival of these emissaries means, even if they briefly pretend not to – their son or their daughter is dead, and now something in them will die, too.

The emotional twist here is that it focuses not upon the bereaved, but on the two officers entrusted with the task of bringing the bad news. The army term for it is "casualty notification", and unlike other routine jobs it never gets any better. Staff Sgt Will Montgomery (Ben Foster), serving out his last three months of duty after injury in Iraq, has just been recruited to partner Captain Tony Stone (Woody Harrelson), a career soldier who'll show him the ropes. Stone's advice is to do it by the book: recite the boilerplate ("... regrets to inform you"), don't touch or hug, don't try to be their friend. Will reads the manual and prepares to plunge into this "ocean of grief". The first one's terrible. The second one's worse. Steve Buscemi, as the father of a 20-year-old casualty, reacts with such raw anger that you almost flinch from the screen. What's so tragic is that neither party in this awful encounter is to blame. It's the guilt of war, for its cruelly random devastation of people's lives.

The first-time director Oren Moverman knows a thing or two about war, having served for four years in the Israeli military. He also knows how to use a camera, keeping close to the two officers as they walk up to the front doors – so close that the viewer seems to be a third member of the detail, cowering behind their broad backs. Both shaven-headed and goonishly bulked, Foster and Harrelson pitching up on your doorstep might be an ordeal in itself. I worried that this pair were too similar in their intense, bulging-eyed demeanour, but Moverman and his co-writer Alessandro Camon have characterised them both superbly, and the actors respond with some of their most interesting work.

Foster, given to playing psychopaths (Alpha Dog, 3.10 to Yuma), uses his twitchy, squashed-looking features with far more restraint here, his ramrod-stiff body language only unbending at home as he relaxes to the pummelling fury of thrash metal on his earphones. But something flickers in his eyes when he and Stone inform a young woman named Olivia (Samantha Morton) that the father of her young son is dead. Something in her stunned reflexive politeness at the news reaches inside Will and haunts him. It would have been easy for the film-makers to kindle a heartwarming romance between the returning veteran and the tragic widow. Instead, they bide their time and allow the performances to suggest a subtler communion of bereavement. "I missed the man he was a long time ago," she says of her late husband, recalling his war-damaged personality, and one senses Will's own anxiety that he could change in just the same way.

Harrelson's Captain Stone is another lost soul, an on-off recovering drunk who's pleased to act the soldier but, unlike Will, never saw combat. "You a headcase?" he asks Will at the start, and you see how these two hair-trigger types might provoke each other; somehow, they decide to become friends. Stone is a blowhard and a skirt-chaser, a bit like Jack Nicholson in The Last Detail, offering advice to his younger colleague but conspicuously unable to function as a regular human being himself. He probably wouldn't survive outside the army, and deep down he knows it. The film echoes the last scenes of The Hurt Locker, where Jeremy Renner's bomb tech shows how unfitted he's become to civilian life: military existence has annexed him completely. That dehumanising element is dramatised poignantly in a late scene here when Will turns up drunk at the engagement party of his ex (Jena Malone) and proceeds to get drunker. When he rises to make "a toast" the moment feels on a knife-edge, and the nervous counter-toast offered to the country's brave military seems as likely to disgust Will and Stone as defuse their aggression.

Given its sombre themes, it's rather a surprise that The Messenger is so high-spirited and companionable in mood. It makes time for a sardonic crack even in a crisis. When Will and Stone make the long walk to another front door, the neighbours of the bereaved watch them as if they were plague-carriers: "Could be worse," mutters Stone, "... could be Christmas". It's a humane and thoughtful movie about a parent's worst nightmare, and is unlikely to draw any better returns than it did in the US, where it opened more than 18 months ago. People don't want to be reminded that they're living in a country at war, and they certainly don't want to be reminded of it when they're out for a night at the cinema.

Not many were keen to catch The Hurt Locker either until it started picking up awards buzz. The Messenger presents a challenge, too, but hugely repays the effort. It will rate among the most sharply written and best-acted movies of the year.