Yama Jun is an 18-year-old kind-hearted 7th-grade angel in heaven. On his 19th birthday, he was unintentionally summoned by the families of some people who wanted vengeance on those who had wronged them in worse ways. On the same night, the chief 1st-grade angel orders Yama Jun to assist those families in exchange for his memories, but with one condition. That is, he must punish those evil people in the most horrific way possible. Soon after, Yama Jun seeks refuge with the Kim family, who are pure of heart and soul, and he adopts the name Hyun and enrolls in a high school to begin his task. On the other hand, Seo Jun, a 19-year-old high school student, becomes cold and unfriendly following the death of his twin brother Minseok. He then encounters the newly arrived Hyun. Not only Seo Jun but the entire school becomes tense after seeing Hyun. Because Hyun is exactly equal to Minseok in every way. Through this, Minseok's best friend and classmate Taemin begins to suspect Hyun as Minseok in disguise and begins to stalk Hyun, leading him to realize Hyun is not even a human but something else.