The Wrath of Mulgarath: The Spiderwick Chronicles Book 5

Bruised and battered, Jared, Simon, and Mallory return home to find the mansion ransacked and learn that Mulgarath has made off with both the Spiderwick Guide and their mother! With only the help of Thimbletack, Hogsqueal, and Byron, the Grace kids have to defeat Mulgarath and his goblin army. But before they can face Mulgarath, they'll have to rescue Arthur Spiderwick from Lorengorm and the elves.