In 1928, Arthur Spiderwick (David Strathairn) wrote a field guide to fairies. Afterward, he hid it in fear of Mulgarath (Nick Nolte), a shape-shifting ogre who has the power to use the book’s secrets for evil. Eighty years later, a divorcée named Helen Grace (Mary-Louise Parker) moves into the abandoned Spiderwick Estate with her children—a daughter named Mallory (Sarah Bolger) and the twins Jared and Simon (both Freddie Highmore). Jared is angry about moving there and would rather live with his father Richard (Andrew McCarthy). He discovers a hidden dumbwaiter which takes him to Arthur’s hidden study, where he finds the field guide. His family doesn’t believe any of it. The next morning, he meets a brownie named Thimbletack (voice of Martin Short), who is there to protect the book from Mulgarath and is angry with Jared for finding it.
But Jared mollifies him with crackers and honey and he gives Jared a stone with a hole in it, through which he can see invisible fairies, and he tells Jared about the protective mushroom circle around the house. Then he sees Simon being abducted by Redcap (voice of Ron Perlman) and the other goblins. Simon is taken to the goblins’ campsite, where he is confronted by Mulgarath disguised as an old man. Jared sneaks in to save him and meets the hobgoblin Hogsqueal (voice of Seth Rogen), who gives him the power to see fairies without the stone. He wants Simon to help him get revenge on Mulgarath. Mulgarath releases Simon so he can get the book. Jared finds him and they fight over the book until they are chased by goblins. They run back to the house and big sister Mallory fights off the goblins with a fencing sabre, doing pretty well considering that she can’t see them yet.
The children are unable to burn the book because of a protective spell over it, so they decide to visit Arthur’s still-living daughter Lucinda Spiderwick (Joan Plowwright) for advice. Simon distracts the goblins while Mallory and Jared escape with the book through a subterranean tunnel. They are pursued by a troll, which is struck and killed by a truck, and they escape. Jared and Mallory meet the elderly Lucinda in the psychiatric hospital where she lives surrounded by sprites. She tells them they need to find her father so he can destroy the book. The trouble is, he has been held prisoner by sylphs for eighty years. Redcap and the goblins come in through the window and in the struggle for the book, tear off several pages, in which Mulgarath finds information on how to break the protective circle.
While Helen is driving them home, she and Jared argue over the existence of goblins. He tells his mother he hates her. Hogsqueal knows of Mulgarath’s plan and gives Simon and Mallory the ability to see goblins and fairies. Jared tries to call his father, but Mallory informs him that his father has moved in with another woman and won’t be coming back. Jared regrets his outburst to his mother. Jared, Simon, and Mallory use the book to summon a gryphon, which takes them to the sylphs’ realm, where they meet Arthur, who has not aged a day. Jared asks him to destroy the book but they discover that Thimbletack has switched the pages with a cookbook. They tell Arthur that Mulgarath knows how to break the protective spell. Arthur helps the children escape under the noses of the sylphs.
At home, Helen has seen Thimbletack and the children are able to convince her of the truth. The goblins spread a potion under a full moon and break the protective circle, but the family defends the book with tomato sauce and salt—deadly to goblins—killing Redcap. Richard appears, saying that he has come home to stay with his children, but Jared sees through the ruse and stabs him. He is Mulgarath in disguise. He corners Jared and the book on the roof. Jared tosses the book and Mulgarath turns into a raven to catch it, but Hogsqueal eats him. Jared, Simon, Mallory, and Hogsqueal gather up the scattered pages. Weeks later, the family brings Lucinda to visit Thimbletack and the old house. The sylphs bring Arthur, but he can’t stay too long or he will turn to dust. Lucinda goes back with him, transformed into a child (Jordy Benataar). The family recovers its normal life with Thimbletack, Hogsqueal, and the gryphon.
The film was directed by Mark Waters, based on the book series by Holly Black and Tony DiTerlizzi, produced by Nickelodeon Movies and distributed by Paramount. It received positive reviews, particularly for Freddie Highmore’s dual role. It was nominated by the Visual Effects Society but lost to The Curious Case of Benjamin Button. Most of the movie takes place in one day. ILM worked on this movie along with Harry Potter and the Prisoner of Azkaban, and Buckbeak’s head was that of the gryphon in this movie as well. Ron Perlman’s voice is not credited. Nick Nolte is on screen for only four minutes, though his voice is used throughout. Sarah Bolger trained three hours a day with the Canadian Olympic Fencing Coach and in front of a blue screen the rest of the time, slicing and chopping things that didn’t exist. It has been pointed out that this movie and The Evil Dead have the same plot.