Nick and Laurie thought their giant problems were solved after they lured all the giants into the sea. But now, the Grace kids are back to tell them they may have caused more trouble! It turns out the giants control the population of Hydra, a dragon-like creature that creates sinkholes all over Florida. But with the mermaids refusing to return the giants to the shore, Taloa still demanding their help in looking for her lost sisters, and the threat of Florida's destruction drawing closer, the kids have to take matters in their own hands. Will Nick and Laurie be able to stop the chaos they unwittingly caused? Is the giant hunter Noseeum Jack really as helpful as they thought? Can Arthur Spiderwick's infamous Field Guide help them out of this mess? Find out in this final instalment Beyond the Spiderwick Chronicles series!