Randy (Randolph) Bragg lives in the small Central Florida town of Fort Repose and appears to be drifting down a somewhat aimless path in life. His older brother, Colonel Mark Bragg, an Air Force Intelligence officer, sends a telegram ending in the words, "Alas, Babylon", a pre-established code between the brothers – a reference to the book of Revelation 18:10, and a warning of impending disaster. Mark is flying his family down to Fort Repose for their protection while he stays at Strategic Air Command headquarters at Offutt Air Force Base in Omaha, Nebraska.
Soon afterward, an American fighter pilot, attempting to intercept an enemy plane over the Mediterranean, inadvertently fires an AIM-9 Sidewinder heat-seeking missile that goes off course and hits an ammunition depot in Latakia, Syria, resulting in a large explosion. This event becomes the apparent excuse for the Soviet Union to launch a nuclear strike against the United States and its allies. The following morning, Soviet missiles are fired over the Arctic, as well as from submarines. American missiles are sent in response. Randy and his guests awake to the shaking from the bombing of nearby air force bases and naval air stations; one explosion temporarily blinds Peyton, Randy's niece.
At first, things are chaotic: tourists are trapped in their hotels, communication lines fail to work, the use of the CONELRAD radio system exposes its weaknesses, convicts escape from prisons and a run on the banks results in all of the banks closing. Randy organizes his neighbors to provide housing, food, and water for themselves.
As the months wear on, news trickles in by radio. Most of the government, on both sides, has been eliminated. The current American president, Josephine Vanbruuker-Brown, formerly the Secretary of Health, Education and Welfare, addresses the surviving United States, noting she is one of the most junior cabinet officials, as everyone above her is dead. Since Randy was an Army Reserve officer before the Soviet attack, he organizes a community self-defense team against bandits and tries to rid the community of radioactive jewelry smuggled into Fort Repose from the radioactive ruins of Miami.
The following year, Air Force helicopters arrive at Fort Repose. When they offer to evacuate the residents from Florida, which is considered a "contaminated zone", the residents choose to stay. It is revealed that the United States won the war, but at a tremendous cost. It is now receiving aid from third-world countries, such as Brazil and Venezuela.