Film archivist David has been having a rough time lately, as he suspects that his wife Alice has been cheating on him with Alex, one of her work clients. This stress is compounded when David's work partner Claire gives him a reel of footage to be archived that shows that his house was the setting for a brutal murder in 1902. David's fears are confirmed when he follows Alice after work and sees her have sex with Alex. Devastated, David grabs a hammer but, coming to his senses, throws it into a nearby canal. Feeling sick, he rushes to a nearby public toilet that his son Billy believes to be haunted, where he vomits. A creepy voice whispers unintelligibly to him and, before passing out, David sees what he believes to be a ghostly figure murder his wife.When Alice does not return home he contacts the police. When Detective McNamara questions him, David denies knowledge of the affair and does not mention the events at the canal. The police eventually find her body at the bottom of the canal, though they rule her death accidental. As David grieves, he becomes obsessed with a series of unsolved, 100-year-old murders that took place around the canal and his home, worrying Claire and putting an increasing strain on his relationship with Billy's nanny, Sophie. David's behavior grows erratic, and he borrows early 20th-century cameras to shoot footage around his home and the canal, where he hopes to capture evidence of supernatural activity. After becoming convinced he has seen ghosts, he moves Sophie and Billy out of his house and into a hotel room.During a video chat with Billy, David sees a ghost in the background, and he breaks into the hotel room, frightening Sophie. David moves them back into the house, but when David is unwilling to explain his behavior, Sophie tells him that she plans to quit in the morning. That night, Sophie is assaulted. David grabs her and locks her in a closet with Billy as he searches the house. Now on his own, David turns to Claire for help in developing footage; she reluctantly agrees. When the police find the hammer in the canal, they become suspicious that David murdered his wife. David's lawyer is able to broker a deal in which Billy will not be taken from him until the results of a psychiatric examination, though David refuses to follow through with it.Claire drops by David's house to deliver the developed film stock, and he convinces her to watch it with him. Though she at first says she sees nothing, she is frightened by a ghostly figure that approaches closer and closer, until it emerges from a hole in the wall. The ghost strangles Claire, and David flees, only to run into McNamara, who was watching the house. The policemen chase David as he flees with Billy into a hidden tunnel that leads to the canal. David, who believes the tunnel was used by devil worshipers to sacrifice local children, is flooded with memories as he sees a ghostly version of his wife: the voice in the toilet ordered him to kill his wife and, in a rage, he drowned her in the canal. When Claire saw nothing on the footage, he strangled her himself.When David reaches the canal, a ghostly figure pulls him under. He does not fight it, though he helps McNamara rescue Billy. Following David's death, Billy's grandmother sells the house and takes custody of Billy. As Billy runs into the house to fetch a toy, David's ghost appears from behind the wall and tells Billy that they can be together forever in the house if he follows instructions; Billy jumps out of his grandmother's car as they drive down the road. Back in the house, the real estate salesperson smiles as she sees Billy run upstairs and slam a door.