Nanny McPhee and the Big Bang

Isabel Green is driven to her wit's end by her hectic life while her husband Rory fights in World War II. Between trying to keep the family farm up and running and her job in the village shop, run by the slightly mad Mrs. Docherty, she also has three boisterous children to look after, Norman, Megsie and Vincent. When her children's two wealthy, but pompous and snobby city cousins, Cyril and Celia, are evacuated to live with them in the countryside, they start fighting with them, only adding to Isabel's problems.

When the magical Nanny McPhee arrives to help, the children at first do not listen and carry on fighting, which she soon puts a stop to with her magic. Meanwhile, Isabel's brother-in-law Phil has gambled away his half of the farm, and is being chased by two hired female assassins working for casino owner Mrs. Biggles. He desperately attempts to make Isabel sell her half of the farm, using mean and spiteful schemes to leave her no choice; one of the schemes, setting loose a litter of piglets to be sold to a neighbouring farmer, is discovered by the children, leading them to bond as they work together to fix it. Isabel takes everyone on a picnic as a show of thanks, during which Mrs. Docherty's ARP Warden husband warns them about bombs and relates how he imagines a pilot might accidentally release one, and Phil subsequently delivers a telegram saying Rory was killed in action. Everyone believes the news except Norman, who is sure his father is alive because he "can feel it in [his] bones". He tells this to Cyril, who at first thinks he is just upset, but then agrees that Norman might be right; the two convince Nanny McPhee to take them to the War Office in London, where Cyril and Celia's father Lord Gray holds an important position, believing he will know the truth.

At first Lord Gray sneers at Norman's disbelief at his father's death, but after Cyril reveals that he knows he is divorcing their mother and blasts him for his neglect as a parent, Lord Gray investigates what has happened. While he is gone, Norman asks Cyril where he will live following the divorce; upon learning Cyril rarely sees either of his parents, Norman says that he and Celia are welcome to live permanently with the Greens. Lord Gray returns and tells Norman that his father is merely missing in action, and that there is no record of a telegram being sent to his mother. After the boys leave, Norman deduces that Phil forged the telegram.

While the older boys are at the War Office, Megsie, Celia and Vincent try to stop Isabel from signing Phil's papers and selling the farm by creating distractions such as pretending that a mouse was in the kitchen. Just as she is about to finally do so, a German pilot accidentally drops a huge bomb on the Greens' barley field; it does not explode, but the fallout is strong enough to cover Phil's papers with ink. When Nanny McPhee, Norman and Cyril return, Phil admits to Norman's accusation of forgery and is handcuffed to the stove by Isabel. The children go out to watch Mr. Docherty defuse the bomb, but when he faints, Megsie takes over, succeeding with the help of the other children and Nanny McPhee's jackdaw friend Mr. Edelweiss. Nanny McPhee helps to harvest the barley with a little magic, saving Phil from Mrs. Biggles' hitwomen in the process. While everyone celebrates, Mrs. Docherty is revealed to be baby Agatha from the first film and to remember Nanny McPhee, who has been staying with her. As Nanny McPhee walks away from the now-happy Isabel and the children, they chase after her, only to see Rory, with an injured arm, making his way back to them. He runs to his family and they embrace.

In a mid-credits scene, Ellie, an elephant conjured by Nanny McPhee to share Vincent's bed, is seen enjoying the magically operated Scratch-o-matic invented for the piglets.

• Emma Thompson as Nanny McPhee, the nanny who changes the lives of the Green and Gray children.
• Maggie Gyllenhaal as Isabel Green (née Carrington), the frazzled mother of Norman, Megsie and Vincent.
• Rhys Ifans as Phil Green, Norman, Megsie and Vincent's uncle, Rory's brother and Isabel's brother-in-law, who tries to sell the farm because he gambled it away at a casino.
• Asa Butterfield as Norman Green, the eldest of the Green children.
• Lil Woods as Megsie Green, the middle and only girl of the Green children.
• Oscar Steer as Vincent Green, the youngest of the Green children.
• Eros Vlahos as Cyril Gray, the spoiled cousin of Norman, Megsie and Vincent. He becomes kinder throughout the film and makes friends with Norman.
• Rosie Taylor-Ritson as Celia Gray, the other spoiled cousin of Norman, Megsie and Vincent. She also becomes kinder throughout the film and makes friends with Megsie.
• Maggie Smith as Mrs. Agatha Docherty (née Brown), the owner of the shop at which Mrs. Green works. In a plot twist at the end, she's revealed to be baby Aggie from the first film, now an old lady.
• Ewan McGregor as Rory Green, Isabel's husband, Phil's brother and the father of the Greens, away fighting in World War II.
• Ralph Fiennes as Lord Gray, Cyril and Celia's father, a General very high up in the War Office.
• Sam Kelly as Mr. Algernon Docherty, Mrs. Docherty's husband, who's an ARP (Air Raid Precautions) Warden.
• Sinead Matthews as Miss Topsey, a henchwoman of Mrs. Biggles, the woman who owns the casino at which Phil gambled the farm away.
• Katy Brand as Miss Turvey, the colleague of Miss Topsey.
• Bill Bailey as Farmer MacReadie, the farmer who buys the piglets from the Greens.
• Nonso Anozie as Sergeant Ralph Jeffreys - the guard at the War Office, and a former charge of Nanny McPhee.
• Daniel Mays as Blenkinsop - Cyril and Celia's chauffeur.
• Ed Stoppard as Lieutenant Addis, a coworker of Lord Gray.
• Toby Sedgwick as an enemy plane pilot.

A third film, to be set in 21st-century England, was planned,[16] but the sequel did not meet studio expectations and plans for any future films were cancelled.[17]

The film had a large number of footage/deleted scenes that ended up on the cutting room floor; unfortunately, only a fraction of it has been released to the public.

The Scenes are:

Vincent Singing in the Barn

Norman Laughing

Shots of Celia Gray in the Mud

a Close up of the Car.

Straw throwing scene from the trailer that was not in the film.

Norman starts up the tractor before going to the field before being confronted by Phil.

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