Fifteen year-old Nell bears an uncanny resemblance to King Edward the Third's daughter, Princess Joan. The king brings Nell and her brother George from the murky steets of 14th-century London so that Nell can be the body double for the princess in times of danger. But the plague takes the princess' life. Nell is forced by Joan's brother, the Black Prince, to continue being the princess. The Black Prince wants Nell to expand the empire by marrying the Prince of Castille. Nell is determined to return to England and report the princess' death to the King.