In the summer of 1876, Mark Twain started to write Adventures of Huckleberry Finn as a detective novel surrounding the murder of Huck's father, Pap Finn. The case is unresolved in the novel as it exists today, but Twain had already planted the clue to the identity of the killer. It is not the various objects ostentatiously left around Pap's naked body; they are not the foreground of the scene, but actually the background, against which a peculiar absence emerges distinctively-Pap's boots, with a "cross" in one of the heels, are gone with his murderer. The key to the mystery of Twain's...