Randy Bragg is a man who lives a life with little purpose. This changes when his brother, Colonel Mark Bragg, sends him a telegram with the code words "Alas, Babylon"—their private code for disaster. Mark, who is on the Air Intelligence staff of the Strategic Air Command (SAC), is certain war between the United States and the Soviet Union is imminent. He sends his wife Helen and children Ben Franklin and Peyton to stay with Randy in Fort Repose, Florida. Randy and his houseguests are awakened by shaking. "The Day" has begun. When the Air Force makes contact with Fort Repose, the community has survived, but at a cost.