Following his discovery of the body of his wife Alison in a bathtub after her apparent suicide, Dr. David Callaway, a
psychologist, decides to move with his 9-year-old daughter Emily to
upstate New York. There, Emily makes an imaginary friend she calls "Charlie". Her friendship with Charlie begins to disturb David when he discovers their cat dead in the bathtub, which Emily claims was a victim of "Charlie". David has nightmares of the New Year's Eve party that occurred the night before Alison's death. When family friend Dr. Katherine Carson comes to visit David, Emily reveals that she and Charlie have a shared desire to upset her father. David meets Elizabeth Young, a local woman, and her niece Amy, who is the same age as Emily. Hoping to cultivate a healthy friendship for Emily, David arranges for a play date. Amy is eager to become friends and gives one of her dolls to Emily, but the play-date is spoiled when Emily cuts up the doll's face. Emily tells David that she does not need any friends. David invites Elizabeth to dinner, where Emily acts hostile toward her. Elizabeth tries to make peace with Emily, but when Emily tells her that she is playing hide-and-seek with Charlie, Elizabeth indulges her by pretending to look for Charlie. When she opens the closet, someone bursts out and pushes her out the window to her death. David asks Emily what happened, but Emily claims that Charlie killed Elizabeth and forced Emily to help him move the body. She tells David the location of the body, but David discovers Elizabeth in the bathtub full of blood (similar to how Alison died). Armed with a knife, David goes outside, where he meets their neighbor and assumes that his neighbor is Charlie. He cuts the neighbor, and the neighbor calls the police. Back in the house, David finds that although he has been in his study many times, the boxes were never actually unpacked after the move. He realizes that he has
dissociative identity disorder and that Charlie is his
alter ego. Whenever "Charlie" would emerge, David would be in his study. He also finally recalls the New Year's Eve party the night before his wife's death. He had caught Alison kissing another guest. "Charlie" was created as a way to express David's rage so that he could murder his wife, something the docile David was too decent to do. Emily knew the entire time about her father's
split personality but did not tell him because she was unsure which personality murdered her mother until "Charlie" killed Elizabeth. Once David realizes the truth, he becomes completely consumed by Charlie, leading him to murder the sheriff who arrives to investigate the neighbor. Emily calls Katherine for help, tricks Charlie, and escapes into the cave where she originally met Charlie. Katherine takes the gun from the dead sheriff and finds Charlie in the cave, who pretends to be David and attacks her. Katherine begs David to fight his murderous alternate personality, but Charlie says that David no longer exists. Emily emerges, begging Charlie to let Katherine go. Her distraction allows Katherine to shoot Charlie, killing him. Subsequently, Emily is preparing for school in her new life with Katherine. Emily's drawing of herself with two heads suggests that she might also have dissociative identity disorder. ==Endings==