Machine Gun Preacher is the story of Rev. Sam Childers, and will be based on his autobiography, Another Man's War. A biker attracted to drugs and violence, he experienced a religious awakening. After a trip to Sudan, he made it his life's work to rescue and protect children from Joseph Kony's Lord's Resistance Army. You can learn more about him and his work on Childers' official website.
Monaghan will be playing Sam Childers' wife, Lynn. According to DHD, Childers' wife was faced with fighting her own demons while Childers' tended bar, kept their family together, and defended children in the Sudan. Shannon will be playing a personal friend of the family, who stayed with Lynn while Sam was away. It's a "pivotal role", those who have read Childers' autobiography probably know more about the familial details.
Machine Gun Preacher was announced as Butler's next big double-duty project, which will see him starring and producing. Marc Forster will sit in the director's chair. Financing was touch and go for awhile, but now it's all secured, and the film will go before cameras this June. I imagine you'll see sunburned Butler paparazzi shots within hours of production starting, though I hope Machine Gun Preacher might be the film that puts an end to his gossipy rom-com days.