Geon-woo, who lost his mother and is living with his stepfather Lee Hyun, who is only 15 years older than him, is his only family, but he has never truly thought of himself as his father, so one day, while he was doing something like that, he found suspicious traces left on Lee Hyun's body. Geon-woo, who thinks it's a bit weird to do something like that without even thinking about a wedding ring, is distraught with Lee Hyun's thoughts all day. In the end, while secretly searching Lee Hyun's room, Geon-woo finds a bright red rope that has a strange purpose to look at?