An experienced detective investigates the murder of a woman, which at first glance seems like a typical crime. However, at the crime scene, he finds a strange note that says, "You're not alone." This affects him deeply. As he dives deeper into the investigation, he begins to feel that he is not just solving a crime, but becoming part of a game in which his reality is slowly distorted. The further he goes, the stronger the feeling that someone is watching him. And, more strangely, this someone se