In 2005, Katie delivers a box of old videotapes to her pregnant sister, Kristi, and Kristi's husband, Daniel. A year later, Kristi and Daniel's house is seemingly burgled and the tapes are missing.
In 1988, a young Katie and Kristi live with their mother, Julie, and her boyfriend, Dennis; Kristi begins interacting with an invisible friend named Toby. Dennis notices that since Kristi's friend appeared, strange things have been happening in the house. Dennis and Julie try to make a sex tape, but are interrupted by an earthquake. While they look for the girls, the camera shows dust fall from the ceiling and land onto an invisible figure in the room. The figure then moves and the dust falls to the floor.
While reviewing the footage later, Dennis notices the strange incident. He invites his friend Randy over to view the footage, who suggests that Dennis place cameras throughout the house to capture any other incidents. That night in the girls' bedroom, Kristi wakes up and begins talking to someone off-camera before going back to bed. When Dennis questions her about this the following day, Kristi tells him that it is Toby. After more disturbed nights and strange occurrences, Dennis discovers a strange symbol in the girls' closet. He finds the same symbol on a picture of women in a book about demonology. Dennis explains to Julie that the symbol belonged to a witches' coven that brainwashed girls of child-bearing age into having sons, and then force them to forget. Julie dismisses his claim.
After Kristi falls ill, Julie and Dennis take her to the hospital. Katie is left with Randy, and she asks him to play Bloody Mary with her. They go into the girls' bathroom and say "bloody Mary" three times and turn off the light. When nothing happens Katie insists they try again. Randy is stricken with pain and the lights reveal a large scratch up the side of his body. They try to leave the bathroom but a black figure moves past the door. When Randy tries to leave a second time, furniture is violently thrown around. After Julie and Dennis return,
Randy leaves in a rush.
The invisible demon terrorizes Katie and Kristi, harming Katie and later dragging her into a closet in the girls' bedroom until Kristi agrees to do what it asks. The next day Kristi asks her mother to take them to her grandmother Lois' home but she refuses. After Julie encounters frightening activity herself in the kitchen, she agrees to go to Lois' home. Dennis sets up another camera in the new bedroom. Before bed, Kristi dresses up as a bride, and when asked who the groom is, replies "Toby", upsetting Julie, who never wants to hear that name again. At 1 am, they are awoken by the sound of a car pulling up outside. Julie says the noise is Lois, who has trouble sleeping. After hearing more disturbances, Julie goes to investigate. When she fails to return, Dennis goes to look for her. In the background the camera captures a shadowy female figure. When Dennis returns and picks up the camera, the figure is gone.
He heads out of the room and calls for Julie and the girls but there is no answer. Downstairs, Dennis notices a human silhouette behind a curtain. When he pulls back the curtain nothing is present, but the room he enters has strange imagery on the walls, including the symbol from the girls' room, which had been concealed beneath framed paintings. Noticing that the back door is open, Dennis goes outside to investigate. In the garage he discovers Lois and several other women, all dressed in black. Dennis flees back to the house, with the women in slow pursuit. In the house he finds Julie at the top of the stairs. As he approaches, he sees that she is levitating unconscious above the floor. Her body is thrown at Dennis, knocking him down the stairs. He picks himself up and sees Kristi, then retreats with her into a closet. Something growls and bangs on the door but eventually leaves.
Dennis and Kristi leave the closet. As they walk through the kitchen, Dennis sees women outside in the garden, circling around a bonfire. As they move into the next room they find Katie crying by Julie's body. He approaches Katie from behind slowly, and places his hand on her shoulder. Katie turns and unleashes a demonic scream that throws him to the other side of the room, injuring his leg. Katie runs away. Dennis tries to crawl toward Julie's body but Lois walks in front of him. As Lois looks down onto him, Dennis' body is suddenly and violently contorted, snapping backwards and killing him. Kristi reappears and goes to Lois, who beckons to Katie. As they head upstairs, Kristi calls to Toby. There is the sound of movement and a monstrous growl as the footage stops recording.