In wartime England, the two very spoiled Gray children are being sent to stay in the country with their very numerous and ill-behaved cousins, the Greens. Enter Nanny McPhee, who discovers that Mrs. Green and the children are fighting another war altogether-against scheming relatives intent on taking their farm while Mr. Green is off fighting in the war. Nanny McPhee must use her magic to teach her mischievous charges five new lessons, or losing the farm will be the least of their problems...