8-year-old Kang Gyung-Joon's spirit suddenly becomes transplanted in the body of 30-year-old Seo Yoon Jae. Seo-Yon-Jae is a successful doctor and engaged to high school teacher Gil Da-Ran. Gil Da-Ran just so happens to be the teacher of 18-year old Kang Gyung-Joon. More problems ensue when 30-year-old Seo Yoon Jae falls in love with another woman.

Overview from themoviedb.org