In 1928, Arthur Spiderwick writes a
field guide about the many
fairies he has encountered. After finishing the Book, he hides it away for fear of Mulgarath, a
shapeshifting ogre who plans to use the Book's secrets for evil. Eighty years later, recently divorced Helen Grace inherits and moves into the abandoned Spiderwick estate with her children, 13-year-old daughter Mallory and 9-year-old
twin sons Jared and Simon. Jared is angry about the move and would rather live with his father in New York. After uncovering a hidden dumbwaiter, Jared discovers Arthur's study where he finds the Field Guide. When Jared explains his discovery of the Book and the existence of magical creatures, his family does not believe him. The next morning, Jared meets a
brownie named Thimbletack, who is initially angry with Jared for having opened the book that he needed to protect from Mulgarath. Jared placates him with crackers and honey, and Thimbletack gives Jared a
holed stone that allows Jared to see the normally invisible fairies by looking through it. Thimbletack tells him about the protective
mushroom circle surrounding the house. Jared witnesses Simon's abduction by
goblins, led by
Redcap. Simon is taken to the goblins' campsite where he is confronted by Mulgarath, disguised as an old man. Jared sneaks into the campsite where he meets Hogsqueal, a
hobgoblin, who gives Jared the ability to see faeries without the stone by spitting in his eyes so he can help him get revenge on Mulgarath for killing his family. Mulgarath releases Simon so he can fetch the book for him. Jared finds Simon and both fight over the book before they are chased by the goblins. The twins flee back to the house, and Mallory fights them off with her
fencing sabre. The children decide to visit Arthur's daughter, their great-aunt Lucinda Spiderwick, for advice. While Simon distracts the goblins, Mallory and Jared escape through an underground tunnel. Chased by a mole
troll sent by Redcap, they narrowly escape when it is struck and killed by an oncoming truck. Jared and Mallory meet the elderly Lucinda in the
psychiatric hospital where she lives, surrounded by
sprites. She tells the children that they need to find her father and have him destroy the book and that, for eighty years, Arthur has been held captive by the
sylphs. At that moment, Redcap and his goblins attack them through the window and manage to tear off several pages from the book before being driven off. Among the stolen pages, Mulgarath is pleased to find information on how to break the protective circle and plans to create a potion in order to do so during the night of a full moon. While Helen is driving home, she and Jared argue over her disbelief; Jared angrily tells Helen that he hates her and does not want to live with her anymore. Later, Hogsqueal, having overheard Mulgarath's plan, informs the children. When Jared tries and fails to contact his father again, Mallory tells him the truth: he's dating another woman and has moved in with her. Jared, Simon, and Mallory use the book to summon a
griffin, which takes them to the sylphs' realm. There, they meet Arthur, who has not aged and is initially unaware of the time he has spent there. Jared asks him to destroy the book only to find out that Thimbletack had switched the pages and kept the real Book. Arthur is relieved until Jared tells him that Mulgarath knows how to break the protective circle. Arthur informs Jared that the sylphs will not allow them to leave as they, like him, know too much about the fairies and the fairies do not want them to reveal their existence to the world. Arthur helps them escape by distracting the sylphs with the fake book. At home, the children finally convince Helen of the truth. Meanwhile, the goblins finish spreading their potion, which successfully breaks the circle as the full moon rises. The family defend themselves with kitchen knives and tomato sauce/salt bombs (ingredients deadly to goblins) and manage to kill the goblins in an explosion of tomato sauce. Suddenly, the children's father, Richard, appears; however, Jared, suspicious about his father's words and behavior, stabs him, revealing him to be Mulgarath in disguise. Mulgarath pursues Jared and the Book throughout the house before cornering him on the roof. Jared tosses the Book and Mulgarath transforms into a raven to catch it, but he is suddenly snatched and eaten by Hogsqueal. Afterwards, Jared and his mother reconcile. Jared refuses to live with his father again and decides to only live with his mother instead. Several weeks later, the family brings Lucinda to visit the house. The sylphs arrive with Arthur, allowing him to briefly visit now that the Book is safe. However, Arthur cannot stay long as he will turn to dust if he remains. Lucinda asks to go with him and is transformed back into a child. The Grace family watch as the sylphs spirit Arthur and Lucinda away, and they are now free to continue and live happily in their new home. ==Cast==