The Wrath of Mulgarath

Spiderwick Chronicles #5 

Bruised and battered, Jared, Simon, and Mallory return home to find their mansion ransacked—and discover that Mulgarath has taken both the Field Guide and their mother.

With only Thimbletack, Hogsqueal, and Byron to help them, the Grace children must find a way to defeat Mulgarath and his goblin army. But before they can face their enemy, they’ll first have to rescue Arthur Spiderwick from Lorengorm and the elves.