The Ironwood Tree
The fourth book in the Spiderwick Chronicles.
With the disappearance of Arthur Spiderwick's Field Guide, the Grace children were hoping the faerie world would finally leave them alone. But then a pack of smelly goblins snatch Simon and a band of elves try to entrap Jared and it's clear that the magical creatures are still keeping an eye on the three siblings.
So when the children notice unusual activity near the abandoned quarry just outside of town, they decide to investigate only to discover a creature with plans to rule the faerie world... whatever the cost...