Kang Bin, is a teacher who has never been in a relationship, but misses the opportunity and is transferred to his alma mater in his hometown. After an accident, he realizes that the place he wakes up to is his alma mater 15 years ago, and there he meets himself and his friends 15 years ago... and his first love. At first, he thought of this unbelievable situation as a dream, but he thinks it was a reality and an opportunity given by heaven. Unimaginable fantasy mystery romance!