In Woo and Tae Hee are two college freshmen who didn't believe in love at first sight but later find themselves wrapped in a deep relationship that would last forever. One day they vow to make their love eternal by sealing it with a bungee jump. But their promise is never fulfilled when Tae Hee suddenly disappears out of In-woo's life for what seems like an eternity. Seventeen years later, In Woo is still unable to get Tae Hee out of his mind even though he's married and has a loving family. While giving a lecture to his students, In Woo is reminded of the memorable times he spent with Tae Hee when one of the students asks about his first love experience. From this point on, In Woo thinks nothing of it until the student rehashes habits and sayings that are so reminiscent of Tae Hee. Clinging to his hope that he will meet Tae Hee once more, a strange mystery unfolds as In Woo tries to discover who this student really is.
