A suburban mom (Charlize Theron), at the end of her rope when child No. 3 comes along, resorts to the services of a “night nanny” (Mackenzie Davis) to ease her burden. The nanny goes above and beyond, even sleeping with the wife’s husband (Ron Livingston) to revive their languishing sex life. Writer Diablo Cody, with her ear for clever dialogue and eye for revealing detail, and director Jason Reitman, with his flair for bringing order out of clutter and confusion, craft a diverting (if familiar) portrait of parenthood, and especially motherhood, as nothing less than hell on Earth, requiring the superhuman—even supernatural—to cope with it. Theron is wonderful, sympathetic even when she’s being unreasonable, and her joined-at-the-hip chemistry with Davis makes the movie’s unsurprising surprises work.