Kyungsoo meets his ex from high school. They rekindle old memories and unravel a 10 year long misunderstanding.    

When they arrive at the apartment building, Seulgi and Yesol press the house number of their sister’s unit and wait for the telltale buzz that will let them into the building. They take the elevator and get off at the right floor, walk to the end of the hallway as instructed and knock at the third to the last door. When it opens, the woman on the other side isn’t their sister.