Directed by Marc Forster. Starring Gerard Butler, Michelle Monaghan, Michael Shannon, Kathy Baker, Souleymane Sy Savane 15A cert, gen release, 129 min

WITH A title like that you were, perhaps, hoping for a gung-ho slab of exploitation in the fashion of Hobo with a Shotgun. A gang of maniacs murders the vicar's wife and he sets off in search of bloody revenge. Sounds plausible. We are, after all, talking about that Gerard Butler.

Marc Forster's film is, as it turns out, a variation on that ancient Pat Boone Bible-thumper The Cross and the Switchblade. Machine Gun Preachertells the true story of a reformed biker and drug fiend from Pennsylvania named Sam Childers. After committing one assault too many, Sam finds God and sets to reforming the world with nail-guns and, well, gun-guns. He builds a church in his hometown, before travelling to Sudan and constructing an orphanage.

Sam, a pretty robust sort of Christian, soon realises that the word of God alone will not repel the rampaging guerrillas. The latter stages will not entirely disappoint those expecting Hobo-style mayhem.

The picture doesn’t waste time explaining the emotional mechanics of Sam’s conversion. One minute he’s stabbing pensioners with a hopped-up Michael Shannon; the next he’s quoting the gospels in a nicely ironed shirt.

But Forster, director of Monster's Ball, has a gift for greasy melodrama, and those opening sections do rattle the bones quite effectively. Though he is not much at home to nuance, Butler's gruff Caledonian bellow suits the character quite nicely.

The scenes in Sudan are more problematic. The shots of legless children and adults with mutilated lips verge on the pornographic.

Students of post-colonial atrocity drama will baulk at the cursory sketching of the background to the Sudanese civil war. Still, if old-fashioned slices of unreconstructed God-bothering are your thing, Machine Gun Preacherwill do quite nicely.

The poster claims, quite correctly, that “Gerard Butler has never been better”. Did somebody at the back say something about “faint praise”. Shame on you.