4 ideas
A lab-engineered pathogen, MM-88, is stolen for a sale and lost when the smuggling plane crashes in the Alps. As temperatures rise, the agent spreads worldwide, first mistaken for a flu epidemic. Within months nearly everyone on Earth is dead except roughly ten thousand people at Antarctic research stations, where the cold keeps the agent dormant, and the book follows how they reorganise as the last human society.
An automatic nuclear retaliation system is built to fire if it detects an attack, so deterrence survives even the death of its commanders. After humanity is gone, a predicted earthquake could register as a strike and trigger a launch aimed at the few survivors, including Antarctica. The book's point is that a machine built to enforce mutual threat keeps executing its logic after every political reason for the threat has disappeared.
The engineered agent first shows up as a seasonal influenza, and its deaths look like ordinary heart failure. Doctors and governments therefore read it through existing categories and respond too late. The mechanism is misclassification: a novel threat that resembles a known, tolerable one gets treated as routine until the death counts can no longer be explained.
Once the survivors are safe, their main threat shifts from the virus to arithmetic. The population is tiny and overwhelmingly male, which forces a governing council to make collective decisions about reproduction, leadership and allocating people. Looking through this lens shows that a species' survival depends less on individual escape than on whether a remnant can build legitimate institutions to manage scarcity, including over its own bodies.