In 1938, two men held history in their hands. One was Adolf Hitler. The other was British prime minister Neville Chamberlain, who, determined to avoid war at any cost, came to be known as "the great appeaser." But Harry Turtledove, the unrivaled master of alternate history, has launched a gripping saga that springboards from a different fateful act: What if Chamberlain had stood up to Hitler? What would the Nazis' next move have been? And how would...