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.
In The Spiderwick Chronicles Book 3: Lucinda's Secret by Tony DiTerlizzi and Holly Black, siblings Jared, Mallory and Simon, having escaped goblins and trolls, are now being harassed by a house boggart. Mallory thinks the only way to stop the madness is to get rid of the Guide. And the only person who can help them is their strange old Aunt Lucinda.