"The Crown Prince broke off our engagement, but... I was never your fiancée in the first place."

Cannon, a poor baroness, works as a servant for Miss Serenade, the fiancée of the Crown Prince. She is beautiful, but her personality is terribly awful... She is always given unreasonable "tasks." And today, on her final day of work, she is ordered to attend the graduation party in Miss Serenade's place! There, the Crown Prince tells her that the engagement is broken off. ...But why is he telling me!? I'm not your fiancée!?