A butterfly flies from the mountain to the city. Sang-Kyu, who works in a company, buys a house in the suburbs and lives with his wife and daughter, Yun-Jeong. But Yun-Jeong becomes a somnambulist because of the illusion of a butterfly flying to the house. Sang-Kyu happens to know Mi-Wu, a singer, who loves Song Cheol-Ho but wanders in her life after his death. On the other hand, Yun-Jeong regains her consciousness with the help of an English psychicist and a nun. After Sang-Kyu has a sex with Mi-Wu, he falls out of the window and loses his consciousness. As she feels affection for Sang-Kyu, Mi-Wu becomes a butterfly in the soul world and leaves him.