Adam Hitchens, a British
conservationist specializing in plant and fungal life, his wife Claire, and baby son Finn travel to a remote Irish village surrounded by a large forest. While exploring the forest with Finn, Adam stumbles upon an animal carcass with a strange fungal substance that has burst open the body. Adam takes a sample and returns home with Finn while Claire (in the midst of removing iron bars from the upper exterior of their home) has an encounter with a local called Colm Donnelly who seems unhappy that the family has moved in. That night, the window in Finn's room is broken while he is sleeping. While the couple suspects the culprit is Colm in an attempt to scare them away, the police arrive and suggest that a bird flew in. The officers inform them of the legend about the surrounding forest—that is inhabited by "The Hallow", a breed of "
fairies,
banshees and baby stealers". Later, Adam spots strange movement in the woods. The next day Adam and Finn arrive in town to replace the broken window, when they are treated coldly by the villagers who repeat the legend of The Hallow and tell them to put back the iron bars. Colm arrives at the house again, frightening Claire, and warns her to leave before giving her an old book. On the drive back, Adam's car breaks down, and he discovers the fungus substance has entered the engine of his car. As he investigates the rest of the car, something pushes him into the boot and locks him in. Adam hears Finn crying as the car starts to shake, and he manages to break out through the backseats. He finds Finn unharmed but the car covered in scratch marks. Unnerved, Adam and Finn return home on foot as night falls, and Claire tells them about Colm. Adam tells Claire to call the police and arms himself with a shotgun. The power goes out, and they find the house has been ransacked. They decide to flee to the car, whereupon they are attacked by the creatures the villagers have warned them about. Adam, Claire, and Finn drive away, but the creatures cause them to crash into a ravine, and they retreat back to the house. While looking out of a keyhole, Adam is stabbed in the eye by a stinger from one of the creatures and realizes that light repels them. Claire and Finn flee into the attic while Adam goes to start the backup generator. The creatures attack Claire and Finn and nearly stab Claire in the eye too, but Adam is able to start the generator and ward the attackers off. The couple barricades the house and locks Finn in a cupboard. They discover the book that Colm gave Claire is filled with information about The Hallow, including their use of
changelings. One of The Hallow manages to abduct Finn before his parents can stop it, and Adam breaks his leg, knocking himself unconscious. Claire pursues the creature and Finn into the forest and retrieves him safely from a pond. Adam sets his broken leg and, upon Claire and Finn's return to the house, begins to suspect that the Finn that Claire rescued is actually a changeling. Claire refuses to believe this, and the couple fight as Claire notices Adam starting to mutate via the fungus injected into him through the stinger. Claire stabs Adam and panics, fleeing into the forest with Finn. Adam soon follows them as his symptoms worsen, and he grows weak around lights. Claire escapes the forest, running to a nearby house for help. Colm is revealed to be the owner, and he sends Claire and Finn away at gunpoint, claiming that The Hallow took his daughter Cora as well. Adam enters The Hallow's nest and retrieves the real Finn from a fully transformed Cora. Claire fends off a group of The Hallow with a camera flash and reunites with Adam, who convinces her that he has the real Finn. They swap babies before Adam is fatally wounded by one of the creatures. The sun rises, forcing the creatures to retreat and destroying the changeling, proving that Adam was right. Adam dies from his wounds while Claire escapes to the house and cries with the real Finn over Adam's death. Later, a logging company start to cut down the forest, and the fungus substance is revealed to be on several logs being driven away. == Cast ==