Newt's Emerald by Garth Nix
It's her eighteenth birthday, and Lady Truthful Newington - nicknamed 'Newt' - is dreaming of her debut in London, where the streets are filled with eligible young men and magic. Coming of age, she is also to inherit the Newington Emerald, a dazzling gem of mysterious power, last worn by her late mother. When the Emerald is stolen in a magic-infused storm, Newt will do anything to recover it - even disguise herself as a man and ally with the handsome-but-insufferable Major Harnett, who professes to despise womankind and harbours secrets of his own. The two are quickly swept into a perilous adventure, filled with sinister fey and shocking reveals, in which grand balls and witty banter mix with daring escapes and deadly curses - for they discover the Emerald is at the heart of a nefarious plot that leads all the way to the Prince Regent!
