"Nancy's Mysterious Letter" Nancy Drew Mystery Stories, by Carolyn Keen

By mistake, Nancy Drew receives a letter from England intended for an heiress, also named Nancy Drew. When Nancy undertakes a search for the missing young woman, it becomes obvious that a ruthless, dangerous man is determined to prevent her from finding the heiress or himself. Clues that Nancy unearths lead her to believe that the villainous Edgar Nixon plans to marry the heiress and then steal her inheritance.