In-woo and Tae-hee are two college freshmen who did not believe in love at first sight, but later find themselves wrapped in a deep relationship that seemed like it would last forever. One day they vow to make their love eternal by sealing it with a bungee jump. But their promise is left unfulfilled when Tae-hee suddenly disappears out of In-woo's life for what seems like eternity. Seventeen years later, In-woo is still unable to get Tae-hee out of his mind even though he is married and has a loving family. While teaching his students, In-woo is reminded of the time he spent with Tae-hee when one of the students asks about his first experience with love. In-woo thinks nothing of it until the student starts exhibiting habits and using phrases that were idiosyncratic of Tae-hee. Clinging onto his hope that he will meet her again, a strange mystery unfolds as In-woo tries to discover who this student really is.