Helen Grace (Mary-Louise Parker) is a newly divorced woman, who, along with her twin sons Jared (Freddie Highmore) and Simon (Freddie Highmore), and their older sister, Mallory (Sarah Bolger), shifts to the fanciful New England home given to her by her great-aunt Lucinda (Joan Plowright). Aunt Lucinda is now in a rest home, having spent her life in fear of the evil creatures that live in the surrounding woods. Jared, who has serious anger issues over his parents' split, begins to roam around the old house. When he finds some strange things around the house, he begins investigating. During the investigation, he meets a tiny being Thimbletack (Martin Short), who has been protecting the book for decades, and an eager but cowardly hobgoblin Hogsqueal (Seth Rogen). Aunt Lucinda's dad, Arthur Spiderwick (David Strathairn), had documented the unseen world of fairies, sprites and monsters in a book before vanishing 80 years earlier. Shape-shifting ogre Mulgarath (Nick Nolte) covets the book, whose secrets would allow him to take over the world. However, Jared finds the book written by his great, great uncle Arthur Spiderwick. When Mulgarath comes to know that Jared has found the book, he sends his gang of goblins against the family. The three tenacious teens are now forced to shield their secluded pastoral mansion from an attack by the evil ogre Mulgarath.