Structural Readers are graded both by structure and vocabulary in six stages, according to the following principles:
* the structures of the language are introduced in the same order as in the majority of modern coursebooks
* the vocabulary is controlled as in other series , with the important development that words required for special puroses are included freely by a prescribed process of repetition.
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.
Following the war, a radioactive cloud begins to sweep southwards poisoning everything in its path. An American submarine captain is among the survivors left sheltering in Australia, preparing with the locals for the inevitable. Despite his memories of his wife, he becomes close to a young woman struggling to accept the harsh realities of their situation. Then a Morse code signal is picked up and the submarine must set sail through the bleak ocean to search for signs of life.