The Wyrm King

Spiderwick Chronicles #8 

Nick and Laurie thought their troubles were over after they drove the giants back into the sea. But when the Grace kids arrive with troubling news, they realize their actions may have set off something far worse.

It turns out the giants played a crucial role in controlling the population of Hydra, a dangerous dragon-like creature now causing massive sinkholes across Florida. With the mermaids refusing to return the giants to shore, the nixies still missing, and the threat of widespread destruction growing, the kids must find a way to fix the chaos they’ve unleashed.

With the help of the Field Guide, Nick and Laurie set out to stop the disaster before it’s too late—but will they be able to undo the damage they unknowingly caused?