Books with title Lucinda's Secret. Tony Diterlizzi and 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.

Book 2 of The Spiderwick Chroniclesin which Mallory, Simon and Jared ask many questions and discover the fate of the missing cat. The Grace kids are just beginning to get used to Aunt Lucinda's strange old mansion when Simon suddenly disappears. At first Mallory thinks the twins are pulling some kind of prank, but when it becomes obvious that he's been snatched by goblins, Jared and his sister, Mallory, have to rely on the help of a mischievous house boggart, a nasty bridge troll, not to mention a loudmouthed hobgoblin, to get Simon back (and uncover why he was snatched in the first place). With the aid of a seeing stone the true nature of the secret world around them is now revealed. It's important the Grace kids tell their story but the faeries will do everything to stop them...