In a textile factory during closing hours, after an employee named Esther says goodbye to her boss Paul, she encounters a silhouette of a strange looking
witch with claw-like monstery hands when the lights are off, but she cannot see it when the lights are on. After she leaves, Paul encounters the woman as well. He tries to run away and locks himself into an office, but is killed after the lights go out. Some time later Paul's son, Martin, witnesses his mother, Sophie, talking to something in the dark. Sophie notices Martin and comforts him about the event, but as Martin goes back to bed he notices a strange figure in the shadow behind Sophie, and locks himself in his bedroom out of fear. Shortly thereafter Martin begins to have trouble staying awake at school. The nurse is unable to get in touch with Sophie to inform her of this, so Martin's older maternal half-sister (Paul's step-daughter) Rebecca is called in to the school nurse's office instead. A
Child Protective Services agent questions Rebecca about Martin's living conditions, and Rebecca tells the official that Sophie is taking
antidepressants. Martin tells her that their mother has been talking to a woman named "Diana". Rebecca assures him that Diana is not real, and that she had also heard their mother talk to the
imaginary girl when she was a child. Once they arrive at Martin's house, Rebecca gets into an argument with Sophie when she realizes her mother is not taking her medication, but Sophie tells Rebecca she has no right to lecture her, accusing Rebecca of abandoning her like Rebecca's father did. Questioning her mother's sanity, Rebecca takes Martin to her apartment, much to Sophie's despair. That night, Rebecca is awoken by the same shadowed woman that killed Paul. She narrowly escapes an attack when she turns the lights on, making the woman disappear. The next morning, Rebecca notices that the name "Diana" has been scratched into her floor, along with a scratch drawing of a stick figure. She remembers finding the same name and drawing as a child and realizes Diana is real. Rebecca finds a box of medical records and research in Paul's office, which reveal that Sophie was admitted to a mental hospital as a child. While there, she befriended a young patient named Diana, who suffered from a severe skin condition that meant she could not go out in sunlight. It was believed that she was evil and was able to "get into people's heads" since Diana's father committed suicide after Diana influenced him to do so. In the end, Diana was accidentally reduced to ashes by the hospital staff when they tried to perform an experimental treatment on her under intense light. Sophie has a conversation with Martin, who was taken back to their mother by the CPS agent, and she decides to allow Martin to meet Diana after turning the light off. However, Martin is frightened by Diana and runs away from them back to Rebecca's place. Rebecca, her boyfriend Bret, and Martin stage an intervention with Sophie about how she is letting Diana haunt them. Sophie becomes irate but secretly asks Rebecca for help, as Diana will not let Sophie go. The group stays the night at Sophie's, intending to get her help in the morning. To avoid an attack from Diana during the night, they rig the house to be as brightly lit as possible, but this proves useless when Diana cuts the power of the whole neighborhood. She traps Rebecca and Martin in the basement and attempts to kill Bret. Despite being injured, Bret escapes by shining the headlight of his car and drives away. Later, Sophie confronts Diana, trying to tell her to spare her children, but is knocked unconscious by Diana when she tries to take her medicine. In the basement, Martin and Rebecca find a black-light; Rebecca is able to clearly see Diana with it, but realizes it is not powerful enough to ward her off. Bret returns with two police officers. When the officers free Martin and Rebecca from the basement, they also see the shadow of Diana and try to go after her, but she kills them. Rebecca and Martin exit the house, but Martin insists on getting Sophie out as well. Rebecca goes back alone for her mother. As she climbs the stairs, Diana reveals that she killed Rebecca's father years ago because, like Paul, he tried to help Sophie recover from her trauma. She injures Rebecca for trying to do the same, but as Diana prepares to kill her, Sophie, who has recovered, appears with a gun from one of the dead officers and shoots at Diana, who says that can't harm her, to which Sophie replies, "This will. There's no you without me." Sophie has realized she is the tether for Diana to exist in the real world and kills herself to save Rebecca and Martin. As Sophie's body falls, Diana vanishes from existence. After the long night, Bret comforts Martin and Rebecca in an ambulance outside the house; a light flickers inside the ambulance but Bret assures them that Diana is truly gone. == Cast ==