YA Book Read in 80s about power of a lie

As a young teen in the mid-1980s, I remember reading a book that, as I remember it, had a title that was similar to the Twain-attributed quote about how a lie can get around the world before the truth has a chance to put its boots on. I really liked it and have not been able to remember its title, etc. for the life of me. As I recall, it was a bit of a mystery-ish story, set around the time of Twain's books. I believe I got the book from a Scholastic Book sale and think that it had a cover that was a white background with a map and other adventuring-type images on it.

Any suggestions? Thanks in advance.