Mrs. Green (Maggie Gyllenhaal), loses her intelligence between hectic life of maintaining her family farm and her job in the village shop, assisted by a little crazy and a little older Mrs. Doherty (Maggie Smith).
She also has three rowdy children to take care of. To top it all, her husband has to go to war. A kind of war breaks between the children’s cousin Cyril (Eros Vlahos) and Celia (Rosie Taylor-Ritson) and the rowdy children of Mrs. Doherty, when they are sent to reside on their family farms. Nanny McPhee (Emma Thompson) comes into the scene taking charge of the matter. They tolerate each other a lot.
Nanny McPhee and the Big Bang video shows that Mrs. Green's brother in law, Uncle Phil (Rhys Ifans) forces Mrs. Green to sell the farm, as he has lost the farm in gambling. One day Uncle Phil (Rhys Ifans) brings a telegram stating that Mr. Green is dead. Everyone believes the story but James, who is one of the cousins was not ready to believe. He finds out that Mr. Green death is not dead. So, if you want to know more, watch the video here.