When Napoleon Bonaparte died in exile in 1821, he took to the grave a powerful secret. As general and emperor, he had stolen immeasurable riches from palaces, national treasuries, and even the Knights of Malta and the Vatican. In his final days, his British captors hoped to learn where the loot lay hidden. But he told them nothing, and in his will he made no mention of the treasure. Or did he? Former Justice Department operative Cotton Malone isn't...