Recently widowed Mr. Brown (Colin Firth) seeks assistance from a mysterious and rather strange looking nanny when his seven very ill-behaved children get too much for him to handle. The children led by the eldest boy Simon have managed to drive away 17 previous nannies and are adamant that they'll have no trouble with this new one. However Nanny McPhee appears to be no ordinary nanny and things soon start to take a turn for the magical...