First in the Celydon Saga, the novel starts the story of the young heroine, Emily, who has the nickname "Danger Girl." Much to her disgust, she finds herself in the middle of a Cinderella story. Everything she was raised to believe has consisted of lies and half-truths. In the land of Prydein and its empire, Druids are the guardians of Celtic culture and advisers of Queens and Kings. The Patrician class forms the highest aristocracy, and the Equestrian class the gentry and ruling class that fills the ranks of the imperial army, navy, and air corps. Britannia may rule the waves and the clouds, but in the town of Nether Poppleton, nestled in the Yorkshire Dales, it is the University of Celydon and its preparatory school, Four Hallows Academy, that forms the center of Emily's world. When inexplicable things start happening at Marbly Manor, Emily gets blamed and it is up to her, with her cousins, to solve a mystery that turns out to be about Emily herself. Ironically, it is being left behind during the summer holiday with her potty neighbor Sir Brian Botany and his astonishing steam carriage that leads Emily to discover the secret kept from her for all of her fourteen years: A frightening grandmother and her connection to the noble and druidical House of Glass.