Hyo-ju and Gun-tah is step-siblings also known as comedy duo in their school. Hyo-ju falls in love with Su-hyun from cross country challenge. From the relationship, Hyo-ju grow into a woman like a caterpillar growing into a butterfly.
However, she later finds out that Su-hyun had something else in mind about their relationship. Hyo-ju is devastated by the sense of betrayal while Gun-tah is starting to act strange around Hyo-ju. What on earth is going on?