Gil Da-ran is a struggling substitute teacher trying to get her certificate, and engaged to the most handsome doctor in the world, Seo Yoon-jae. It's a fairy tale dream come true until one month before the wedding, Yoon-jae becomes more distant. At the same time, Da-ran meets a young transfer student from the States, Kang Gyung-joon, who's got an attitude towards everyone except Da-ran. But then Gyung-joon gets into a car accident with Yoon-jae, and the two of them drive over the guard rail and into the deep waters. Yoon-jae tries to save Gyung-joon, but in the process, Yoon-jae dies and Gyung-joon ends up in a coma. Gyung-joon soon wakes up...but finds himself in Yoon-jae's body!