Laura Daniels, who works at a dating consulting firm, heads out on a date with lawyer Michael Krasnick. Back at home, her roommate Cindy Matthews uses Laura's Ouija board to contact a 21-year-old named “David” who claims to have been murdered in their New York apartment in 1978. Laura returns to find an assailant strangling Cindy to death. She calls the police, but they arrive to find no body and no trace of a crime, and they cite her for a false alarm. Michael believes Laura but thinks Cindy’s involved in a prank, and soon he notices Cindy has a habit of mysteriously vanishing for long stretches. Laura purchases a house alarm at the mall, only to be chased by Cindy’s murderer.
That evening, Laura uses the Ouija board again and comes in contact with Mark Banning, who claims to have murdered Cindy and announces that he intends to kill her as well. Laura faints, and the next day she visits a doctor for a brain scan, receiving prescription drugs from Dr. Roger Kelton. She is then fired from her job when her boss says her résumé is full of lies. Angry, she goes for a swim to calm down, but is attacked again in the pool. Kelton contacts Michael and tells him that Laura has undergone electroshock therapy in the past and may suffer from schizophrenia or depression. Michael confronts her, though Laura denies Kelton’s claims.
Soon after, Michael uncovers that most of Laura’s life stories appear in a series of children’s books written by another Laura Daniels. After another confrontation, Laura concedes she might be unstable, but Michael believes she’s a compulsive liar and walks away. Laura then visits the library and learns that a Mark Banning was once murdered and immolated in her apartment, and Cindy’s murderer attacks Laura in the apartment with an axe. She calls the police, who no longer believe her, and she must hide in a closet before fleeing. A trip to the police station proves unhelpful, and when she investigates Mark’s death herself, she discovers that his sister, Jennifer, is a mental patient.
When Laura visits Jennifer’s mental hospital, the staff recognize Laura as Jennifer. Nurse Crenshaw explains that Laura escaped from the institution over a year ago after an assault by a man who appears to be Cindy’s killer. In the hospital library, Laura finds Laura Daniels’ children’s books and realizes she had assumed the author’s identity after her escape. Laura checks into a local motel, where Michael shows up to apologize and to try to win her back. After Michael leaves for pizza, the killer attacks Michael in his car and stabs him in the leg before heading to the motel to attack Laura. She bludgeons him with a lamp and flees; as he gives chase, Michael shoots him dead. Laura suddenly realizes the killer is her brother, Mark.
At the police station, Kelton explains that the Ouija board brought out Laura’s subconscious fears of Mark. Laura clarifies that the man killed in 1978 was her ex-boyfriend David, not Mark. Mark, driven by his father’s disapproval of David, killed David and then attempted to trap Laura in the apartment by locking her in a closet and setting the place on fire, a plan that failed when she escaped and fell into a coma. The police assume the immolated corpse belonged to Mark, since the room was registered to him. Michael adds that this still doesn’t explain the messages Cindy received while using the board in another town. The motel’s Ouija board is later found by the property owners; during a power outage caused by a storm, they hear a noise and, startled, the man asks if anyone is there, and the planchette moves by itself to point to “yes.”
