When German troops surround Leningrad and cut off food supplies in the fall of 1941, no one imagines that the siege will last 900 long days and take hundreds of thousands of lives. As the first “hunger winter” sets in, the city’s residents strip the bark off trees, boil and eat moss-covered stones, and trade priceless antiques for half a loaf of bread—and sex for a chunk of sugar. But the scien...