The Strange Case of Dr. Jekylll and Mr. Hyde

The classic psychological mystery. According to Wikipedia: "Robert Louis Balfour Stevenson (13 November 1850-3 December 1894), was a Scottish novelist, poet, essayist and travel writer. He was the man who "seemed to pick the right word up on the point of his pen, like a man playing spillikins", as G. K. Chesterton put it."