The 1940s. With her husband away fighting Adolf Hitler's Nazis, overworked Isabel Green finds herself caught between a hectic life of tending to the family farm and raising three mutinous children. In desperate need of a helping hand and at the end of her tether, Isabel can't believe her eyes when Nanny McPhee, the extraordinary government nanny, shows up at her front door after the events of Nanny McPhee (2005). As Isabel's scheming brother-in-law, Phil, tries to talk her into selling her half of the farm, the poor mother is going to need all the help she can get. Will a sprinkle of good old magic do the trick once more?