“You don’t need to worry about me,” declares Staff Sergeant Will Montgomery (Ben Foster), speaking to his ex-girlfriend after returning home from duty in Iraq. “The world’s my oyster.” But watching Will as he slumps around his apartment, I was reminded of one of Charles Dickens’ masterful metaphors: “as solitary as an oyster.” With his girlfriend gone, Will seems to have no friends, no family to speak of; he sits alone, blaring music, sleeping on the floor, no computer, no life outside the army, cut off from the world he supposedly fought to protect. He’s got three months left to serve, after which…job, college, raising a family, none of the above, who knows? For years now, he’s just followed the mission set in front of him, and he’s gotten awfully good at it.

Now, Will’s been assigned as a Casualty Notification Officer (CNO), informing next of kin (NOK) that their loved ones have been killed in action. Casualty Notification is often described as the most difficult job in the army; I don’t feel qualified to make that statement, but I think I can safely say that it requires a very different skill set from what is usually asked of soldiers. Physical prowess won’t help you here. A CNO walks into the NOK’s life, delivers heart-rending news, and walks right out again. Will sees nothing of these people’s lives except the pain and despair that follows his arrival. He is not allowed to offer any physical comfort; he can only stand there and watch someone else’s life collapse around them, and take the abuse invariably hurled in his direction.

It’s grueling, unrewarding, emotionally draining work, and the only way he can make it through the day is by following protocol, treating his job as a mission just like any other. That’s certainly the attitude taken by the superior officer accompanying Will on his rounds, a gruff, strutting Gulf War vet named Tony Stone (Woody Harrelson). The two are a bit at odds at first (Will just cares a bit too much about the people he’s informing), but there’s nothing like common experiences to bring people together, and getting spat upon by a distraught father is a doozy of a common experience. Foster and Harrelson play well off each other, and it’s extraordinary to watch the friendship between Montgomery and Stone grow ever so slowly, as they find their bond is one of the few things that can keep them going.

One day, the two notify a woman named Olivia (Samantha Morton) that her husband has been killed in Iraq. Olivia seems to affect Will in a way nobody else has yet managed, and it’s not long before he’s spending his free time hanging around her house and offering to fix her car. There are all sorts of ethical questions that come into play here, but this is no morality tale. You could accuse Will of taking advantage of Olivia in her confused, emotional state, and sure, Will is probably looking all too quickly to fill the void left behind by his ex-girlfriend. But there’s something tender and legitimate about Olivia’s behavior towards Will. She works at a storage facility, and likes to take home the “nice things” that other people leave behind: mattresses, coffee tables, framed pictures of strangers, a piano. Keep that in mind when considering her attraction to Will.

There’s a theory that posits if you just let people keep talking, they will eventually reveal their nature, and that holds true here. There are a couple scenes in this film that could serve as a master class for monologue acting; watch Samantha Morton’s face when Olivia describes washing her husband’s shirt, or listen to the pent-up grief and frustration in Ben Foster’s voice as he explains what happened in the firefight that made Will a war hero.

This is the first film directed by screenwriter Oren Moverman (“I’m Not There”), a former Israeli paratrooper and journalist. His style isn’t flashy or manipulative; he languishes in long cuts, letting the superb cast really delve into the writing and explore their characters. The script is remarkably subtle and restrained, especially considering its loaded subject matter. Will lives on the edge, constantly in danger of giving in to post-traumatic stress, but we know this film will never end with a dramatic, 11 o’clock news type of breakdown; Moverman isn’t interested in that kind of preaching.

Instead, we just watch Will Montgomery smolder, a barely suppressed fire, with the occasional spark flashing out and hinting at the incredible pain lying below the surface. As Tony says, he’s seen too much to become an insurance agent or anything like that now. So what will he do? He can let that anger and hurt consume him, burn up the life and future he could still have; or he can just keep going. When you experience that level of agony and destruction, you have to find an appreciation for the little things that make life worth living: a slice of pizza, an e-mail from a good friend, a drink with a buddy or just watching the sun rise.