Today the figure of Sherlock Holmes towers over detective fiction like a colossus, but it was not always so. Edgar Allan Poe's French detective Dupin, the hero of "The murders in the Rue Morgue," anticipated Holmes's deductive reasoning by more than forty years with his "tales of ratiocination." In "A Study in Scarlet, the first of Holmes's adventures, Doyle acknowledged his debt to Poe and to Émile Gaboriau, whose thief-turned-detective Monsieur...