It seems that lightning does strike twice. Zachary Turpin, a doctoral candidate in English at UH, is sort of a literary treasure hunter. Last year he discovered a previously unknown self-help book by Walt Whitman (Manly Health and Training) and now he's done it again, discovering a 36,000-word mystery novel written by the poet. Using modern-day sleuthing tools (online databases of 19th-century newspapers), Turpin searched key words from one of Whtiman's handwritten journals and came upon an 1852 advertisement in The New York Times; he followed the threads and the result, with introduction by Turpin, is finally getting its day in the sun. His M.O. seems to work; he's also discovered lost works by Mark Twain, Emma Lazarus, Ambrose Bierce and L. Frank Baum; Turpin will be on hand this Saturday to sign and discuss Whitman's novel.