Hee-min recently moved to a new school, and on his first day, he falls in love at first sight with a girl named So-young. Hee-min happens to find So-young's diary, and he decides to return the diary to her with Valentine's day candy. In order to do so, on the eve of Valentine's day, Hee-min sneaks into the school afterhours, but eventually realizes that strange things are happening.
