In the extraordinary Worldwar tetralogy, set against the backdrop of the World War II, Harry Turtledove, the "Hugo-winning master of alternate SF" (Publishers Weekly), wove an explosive saga of world powers locked in conflict against an enemy from the stars. Now he expands his magnificent epic into the volatile 1960s, when the space race is in its infancy and humanity must face its greatest challenge: alien colonization of planet Earth. Yet even in the shadow…