In 1941, farsighted Gabriel Cohen, a Belgrade shopkeeper, tied several thousand dinars into a neat package. Then he locked and shuttered his shop, and with his bundle of money under his arm, took a stroll to Belgrade's biggest cemetery. There he held a long conversation with a sexton. The money changed hands. The sexton led the way to a family-sized crypt, which Cohen entered. The crypt's massive door slammed, was locked from the outside. Shortly after, the Germans blitzed Belgrade, then took over what was left of the city.
During the three and a half years they stayed, all but...