MACHINE GUN PREACHER (15, 129 mins) *** Starring Gerard Butler, Michelle Monaghan, Madeline Carroll, Kathy Baker, Michael Shannon, Souleymane Sy Savane. Director: Marc Forster

One man can make a difference in Machine Gun Preacher, based on an inspirational true story.

Unfortunately, that man isn’t Gerard Butler, whose portrayal of thug-turned-guerrilla humanitarian Sam Childers seems to have one eye on awards consideration when the actor should have kept both focused on an emotionally-rich performance.

In truth, the overlong screenplay does Butler few favours, failing to empathise with the lead character as he abandons his family to wage a one-man war in the Sudan when he has pressing responsibilities closer to home.

Nor does it help that while we admire Childers for his self-sacrifice and bravery, we don’t fully understand the reasons for his crusade or see his personal anguish reflected on the big screen.

Director Forster hammers home the horrors perpetrated by Joseph Kony and his Lord’s Resistance Army (LRA) in shocking scenes of slaughter and cruelty.

The film opens with a night-time attack on a village and the sickening image of a young boy forced to bludgeon his weeping mother to death.

On this most primal level at least, Machine Gun Preacher hits hard.

Violent biker Sam Childers (Butler) emerges from prison, seemingly intent on returning to his boozy, degenerate old ways, much to the chagrin of his wife Lynn (Monaghan) and daughter Paige (Carroll).

Then, miraculously, Sam finds God at the church attended by Lynn and her mother Daisy (Baker) and he is deeply moved by a sermon from a pastor who tends to a flock in Africa.

So Sam decides to be good a Christian and travel to war-torn Sudan to build an orphanage for the children who have been caught up in the bloody conflict.

In the process, Sam witnesses shocking acts of brutality perpetrated by the LRA against the boys and girls and he takes up arms to protect them, assisted by Sudan People’s Liberation Army soldier Deng (Savane).

Machine Gun Preacher has its heart in the right place and the true story that underpins this uneven fiction is extraordinary, attesting to the endurance of the human spirit in the face of unspeakable evil.

Butler has fire in his belly but tender moments are lacking, and he spends too long apart from Monaghan to spark sufficient screen chemistry.

Thus, one of their most important scenes has to be conducted over the telephone, with Sam threatening to quit after the orphanage is burned down and Lynn telling him in no uncertain terms to “get off your butt and build it again.”

Behind every great man there is a fierce woman.