Eleven year-old Nick Vargas thinks his sucky life is being turned upside down. His father has just remarried and moved his new wife and her daughter into his home in the soon-to-be-completed, Mangrove Hollow. And now, if it isn't bad enough that Nick has lost his bedroom to his wacky new step-sister Laurie (who lugs around this huge book about faeries), his father actually wants him to spend time with her! So when an "expedition" to a nearby lake turns up a nixie with a giant problem - and by giant, we mean the enormous, fire-breathing kind - it's up to Nick and Laurie (with the help of Nick's older brother and a very familiar face from the original Spiderwick Chronicles) to come up with a plan. Will they be able to stop the rampaging beast before all of Mangrove Hollow goes up in smoke?