Introduction: Hyo-joo lives in a one-room apartment. In fact, the apartment does not have a security problem. One day, he sees that the door of his house is really forced, and when he looks through the door binoculars, he cannot see anyone. Even though he calls the police and asks for help, when the police come to the house, he does not encounter any doubt and danger. And after that he begins to investigate this mystery on his own....