Bullets and bibles: "Machine Gun Preacher"

This is a turn-up - Gerard Butler's first real role, outside that of a smirk with abs. In Marc Forster's drama Machine Gun Preacher, Butler assumes the extraordinary true-life figure of Sam Childers: ex-con and speed-freak biker who, under the influence of his devout wife Lynn (Michelle Monaghan) became first a born-again Christian, then a missionary, rocking up in Sudan in the first years of this century, where he saw at close hand the devastation left behind in the wake of a bloody civil war, and promptly resolved to build an orphanage with his own bare hands. And then, when it burned down, to build it all over again. My sometime comment that Butler has, thus far in his movie career, had the look of a brickie who got lucky is what now makes him exactly right for this part.

To some extent, Childers is but a tweak on that species of bull-headed action figure the star has grown used to playing - the kind of guy who, when he wanted drugs, blasted his way into a squat and took some; the type who, when his family found themselves threatened by a tornado, blasted a hole in the floor of their shack, hid his wife and child there, and then threw himself over the top of it. I doubt there's a job or a region on God's green Earth that Sam Childers didn't think couldn't be fixed with the help of a gun; only when we see him pawning his shotgun collection to buy the orphanage a swing set do we realise quite how serious he is about his new life.

Put this way, Machine Gun Preacher should be utterly preposterous, yet there's a certain degree of fun to be had watching Butler think his way through the contradictions of an individual with a Bible in one hand and a semi-automatic in the other. Sam Childers was fervent, an all-in fellow: he makes mistakes, and sometimes he learns from them and sometimes he doesn't. Butler grants him a dumb likability, and tones down the happy-clappiness: why would you bother clapping the Lord's work, when you can get some of it done yourself with the appropriate firearms?

Everybody else on screen is merely orbiting, but Forster gives them their due when it's required: Monaghan makes the wife role a little tougher than it might have been in other hands, with a run of good scenes when it becomes apparent Sam is torn between his two families - his own, and his kids over there. The wiry Michael Shannon, soon to be seen ripping up the screen in Take Shelter, is a more convincing speedfreak than his buffed male co-star, and his recovery, set in contrast to Sam's, is credibly awkward and erratic. And Souleymane Sy Savane, from Ramin Bahrani's Goodbye Solo, puts enough into his Sudanese liberation fighter to ensure this isn't just another of the award season's white-man-in-Africa fables.

Machine Gun Preacher is such a tall-sounding tale you sense writer Jason Keller has had to compress it a little just to get it on screen; the connecting narrative fabric, explaining how Sam got from A to B, seems scant in places. Yet once he gets past the trailer-park cartoon of the opening act, Forster invests the film with the same middlebrow sincerity that audiences responded to in Finding Neverland and The Kite Runner. The second half gets a little pious and ploddy, as social conscience movies are wont to do, but this is one of those stories that not even a Hollywood in league with the conservative Christian right could entirely ruin: in its better moments, Machine Gun Preacher blindsides you with its faith - with its bold, muscular lunges at portraying human decency and depravity - in a way something as obvious and leadfooted as The Blind Side really couldn't.

Machine Gun Preacher is in cinemas nationwide from tomorrow.