The uninvited guest

The young architect So-jin has not been able to recover from the death of his wife for six months. He lives in his parents' big house, suffers from post-traumatic stress disorder, and has difficulty communicating with his young daughter. Suddenly, Seo-jin gets a call from an orphanage informing him that his younger sister Yoo-jin, whom he lost at an amusement park more than 20 years ago, has been found. The parents happily accept their newfound daughter, and she surrounds them with care, but So-jin finds his sister very suspicious.