David Walliams, hailed as ``the heir to Roald Dahl`` by The Spectator, burst onto the American scene with the New York Times bestseller Demon Dentist . Now the UK's #1 bestselling children's author is back with this high-flying adventure about a boy and his grandfather, perfect for fans of Jeff Kinney and Rachel Renee Russell. Grandpa is Jack's favorite person in the world. It doesn't matter that he wears his slippers to the supermarket, serves Spam a la Custard for dinner, and often doesn't remember Jack's name. But then Grandpa starts to believe he's back in World War II, when he was a Spitfire fighter pilot, and he's sent to live in an old folk's home run by the sinister Matron Swine. Now it's up to Jack to help Grandpa plot a daring escape