Australia is one of the last places where life still exists after nuclear war starts in the Northern Hemisphere. A year on, an invisible cloak of radiation has spread almost completely around the world. Darwin is a ghost town, and radiation levels at Ayres Rock are increasing. An American nuclear-powered submarine has found its way to Australia where its captain has placed the boat under the command of the Australian Navy. Commander Dwight Towers and his Australian liaison officer are sent to the coast of North America to discover whether a stray radio signal originating from near Seattle is a sign of life.