Beyond the Spiderwick chronicles

Eleven-year-old Nicholas Vargas already thinks his life has been turned upside down after his developer father remarries and moves his new wife and daughter into the soon-to-be completed Mangrove Hollow. But when an "expedition" to a nearby lake turns up a little nixie with a giant problem-- the huge lumbering, fire breathing variety -- it's suddenly up to Nick: his stepsister Laurie; and his big brother, Julian, to figure out how to stop all of Florida...

Nick,Julie, Laurie, and their friends try to prevent a hydra from destroying Florida.