During his forced residence, X-127 is ordered to push the bomb buttons to begin World War III (which lasts a total of 2 hours and 58 minutes). From that point, all civilian life (for military personnel already occupy Level 6 and 7) moves from the surface of the earth to a collection of underground shelter complexes (levels 1 - 5). It later emerges that the orders given had been wholly automatic, and the war had taken place as a series of electronic responses to an initial accident. Toward the end of the novel, the surviving shelters are gradually snuffed out, one-by-one, as the surface contamination makes its way down past air filters and into ground water sources. In the end, the inhabitants of "Level 7" are exterminated by a malfunction in their nuclear power pile.
The book is written in such a way so as to make it impossible to determine which side is which. References to democracy are structured as to be just as applicable to the statements made about democracy by the Soviet government of the time. The book contains no geographical references or individual names. The theme of the book is the dehumanisation and abstraction of nuclear warfare, and the danger that this leads to when combined with the destructive potential of the weapons involved. The novel thus acts as a warning against the nuclear arms race, as the original (but removed) postscript makes clear:
Originally, the manuscript contained a preface by Martian archaeologists, who discover the diary amongst the ruins of a destroyed Earth. However, this was removed in editions earlier than 2003, because it was felt that it spoiled the ending of the book.