The door that was attached to a wall was the door that led to another room?! Hosu, who used to move a lot because of his parents' work, finds a strange door in their new house. And he meets Seungwoo, a boy of the same age who lives across the door. The two boys, who shared a mysterious experience, began to come and go through the door. Warm air permeates between the two like a late afternoon. And slowly another secret grows in the hearts of the boys...