After the Nazis force the surrender of Britain and France in 1940, Burton K. Wheeler, running as the Isolationist Party candidate, defeats President Franklin Roosevelt on a pledge to keep America out of war. After Germany has overrun Russia, both Germany and Japan invade the United States in 1941. President Wheeler surrenders the United States to the Axis after a devastating bombardment of missiles from occupied Canada. The surrender takes place on April 20, 1948, Adolf Hitler's fifty-ninth birthday. President Wheeler, Army Chief of Staff General George Marshall, and other U.S. Government officials are executed by garrote in a meat packing plant outside of Washington D.C. after being found guilty of "war crimes."
However, before surrendering, President Wheeler did manage to preserve one spark of hope for the future: he ordered General Buckwesson, who at thirty-eight was the youngest four-star general in history, to set up a secret base in the Rockies known as the National Redoubt, and complete this timeline's version of the Manhattan Project, in the hope that the first atomic bomb would some day help in liberating the country. The base remains intact, undiscovered by the victorious Nazis and Japanese. A group of American Resistance fighters attempt to spark a revolution at a summit meeting between Hitler and Tōjō celebrating the 30th anniversary of the Axis victory in World War II.
The book begins on July 4, 1976. A Japanese general is visiting China Lake, California, the site of his victory over General George Patton during World War II. A bomb planted on a horse explodes, killing the general, and a mysterious cowboy is seen in the area. The cowboy is Cooper, travelling with his adopted father Wayne Stubbs, and a young Native American woman named Chula. They travel to the hidden National Redoubt in the Rocky Mountains, where work on developing a nuclear bomb had been ongoing throughout the decades. However, General Buckwesson, comfortable in his fortress, has no intention of sparking a revolution despite the unique opportunity that has recently arisen. A senile Hitler and a retired Tojo are meeting in the geographic center of the now divided United States. Cooper and younger members of the resistance plan on attacking the event, and Lisa Blum, daughter of the last head of the Manhattan Project, suggests using the only atomic bomb in the world.