Maxwell Smart still feels at his safest when it rains. The 93-year-old first learned this as a boy of 10, alone in a forest, lying on a bed of leaves in a makeshift bunker, waiting out the Nazi occupation of Poland. For two years he hid in the forest, evading hunters. Detection meant likely death. “It was a sport to kill a Jew,” he says. “[Your typical Nazi] is not going to go in the mud and get dirty and filthy; he is doing it for happiness, for enjoyment. So when it was raining, I knew I was safe.” Smart...