Kate is a forensic psychologist who gets the job of investigating the killing of a man who is supposed to have been strangled while sleeping on his own wife, and the only witness to this alleged murder is their eight-year-old daughter, Sophie. While Kate deepens this case and penetrates deep into the mystery, she discovers that an ancient demon may be responsible for this crime – knowing he is killing the victims while they are asleep. As a result, Kate has some terrifying experiences and symptoms like all the other victims of the demon so far and has come to a real nightmare from which she tries to save herself and help Sophie before falling asleep again.