Lucinda's Secret by Holly Black
Book 3 in the hugely popular series, The Spiderwick Chronicles.
Things at the Grace residence are getting completely out of hand. As if being attacked by vile, smelly goblins and almost eaten by a bridge troll wasn't enough, now the house boggart, Thimbletack, is out to get Jared. Simon has a very hungry griffon recuperating in the carriage house, and Mallory is convinced that the only way to stop the madness is to get rid of Arthur Spiderwick's Guide. But with all kinds of creatures after them, the Guide is the only protection the Grace kids have... If only they could work out why the faeries are stalking them? Could it be the Guide that they want? There's only one person who might know the answer ~ their crazy old Aunt Lucinda.
Things at the Grace residence are getting completely out of hand. As if being attacked by vile, smelly goblins and almost eaten by a bridge troll wasn't enough, now the house boggart, Thimbletack, is out to get Jared. Simon has a very hungry griffon recuperating in the carriage house, and Mallory is convinced that the only way to stop the madness is to get rid of Arthur Spiderwick's Guide. But with all kinds of creatures after them, the Guide is the only protection the Grace kids have... If only they could work out why the faeries are stalking them? Could it be the Guide that they want? There's only one person who might know the answer ~ their crazy old Aunt Lucinda.