The Mystery of the Five Hundred Diamonds is a thrilling mystery novel written by Robert Barr. The story is set in London and revolves around the theft of five hundred diamonds from the safe of a wealthy merchant named Mr. Septimus Ralston. The diamonds were kept in a locked safe that was only accessible to Mr. Ralston and his trusted secretary, Mr. James Rigby. However, one day, when Mr. Ralston opened the safe, he discovered that the diamonds were...