As her sick father's last wish, Emilia, the eldest daughter of the Bradley Marquis family, reluctantly accepts her arranged marriage to Mathias, the eldest son of the Karen Border Lord. This is because he has sworn not to cause chaos among the people of the territory due to the lord's death. However, her husband-to-be, Mathias, is unable to attend the wedding due to border defences. As a result, Emilia has a marriage ceremony with Mathias' representative and travels to Vanrosia, her husband's territory. Although it is an unwanted marriage, Emilia is the mistress who will look after her husband's kingdoom while he is away. So when she takes her husband's place and actively promotes the reform of the territory, the change is unexpectedly successful and she spends her days fulfilled. One day, however, her husband, whom she has never seen, finally returns. He has a vow in his heart that Emilia never expected... What will become of their relationship?