The threat of world overpopulation is the latest assignment for Brown's art historian and accidental sleuth Robert Langdon. Awakening in a Florence hospital with no memory of the preceding 36 hours, Langdon and an attractive attending physician with an oversized intellect are immediately pursued by an ominous underground organization and the Italian police. Detailed tours of Florence, Venice, and Istanbul mean to establish setting, but instead bog down the story and border on showoffmanship. Relying on a deceased villain's trail of clues threaded through the text of Dante's The Divine Comedy, the duo attempt to unravel the events leading up to Langdon's amnesia and thwart a global genocide scheme. Suspension of disbelief is required as miraculous coincidences pile upon pure luck. Near the three-quarters point everything established gets upended and Brown, hoping to draw us in deeper, nearly drives us out. Though the prose is fast-paced and sharp, the burdensome dialogue only serves plot and back story, and is interspersed with unfortunate attempts at folksy humor. It's hard not to appreciate a present day mega-selling thriller that attempts a refresher course in Italian literature and European history. But the real mystery is in the book's denouement and how Brown can possibly bring his hero back for more. Agent: Heide Lange, Sanford J. Greenberger Associates. (May)