Set in a fictional country called Daeho that does not exist in history or on maps, it is about the love and growth of young mages as they overcome their twisted fates due to a forbidden magic spell known as the "alchemy of souls", which allows souls to switch bodies. It follows the story of an elite assassin named Naksu, whose soul is accidentally trapped inside the weak body of Mu Deok—Jang Uk's servant from a powerful and noble family in the country. The young master of the Jang Family, Jang Uk, holds a dark secret about his scandalous birth. He wants the formidable assassin to help change his destiny.