The moon mysteriously breaks into seven pieces, destroyed by a traveling black hole or some other unexplained anomaly. At first everyone is just kind of puzzled, but not too concerned. Then, after two of the pieces collide and one breaks, astronomers realize the implications of this unstable gravitational system. The collisions will become more and more frequent, until in about two years there will be so many moon rock meteors entering the Earth’s atmosphere that ambient temperatures worldwide will rise to several hundred degrees. This is what they call the “Hard Rain” and it is not good news for life on Earth.
The book has three parts – one during the preparation for the Hard Rain, the second during the Hard Rain and a few years after (until humanity gets to safety) and the final section about 5000 years in the future, just as mankind is starting to repopulate the stabilized Earth. (I agree with reviewers on Amazon and elsewhere – part 3 is kind of weak; interesting “future history” and some cool mega-engineering projects wrought by our spacer descendants, but the storyline is pretty predictable and ho-hum.)
In its final two years, Earth puts together plans for a “Cloud Ark” of spacecraft, centered on the International Space Station, which will preserve humanity while everyone else dies. Initially I thought it was odd to try escaping high velocity space rocks by going into space, but I guess it kind of makes sense: if you are directly hit by a bolide, whether on Earth or in a spacecraft, you are dead. But, even if many bolides miss you directly, you still get toasted on the Earth due to atmospheric heating. Too bad. So space it is, where at least some of the “arks” will not get directly hit by a bolide.
Pretty soon after the hard rain starts, the ark kind of falls apart, thanks mainly to the interference and ignorance of the ex-President of the USA*. Annoyingly, she is still playing old world politics when the remnants of humanity need unity and the brains in charge in order to survive. Most of the arks split off from the ISS lead and eventually run out of food and turn to cannibalism. The ISS crew ends up seeking shelter in Cleft, the old core of the moon, a voyage which takes several years because orbits and mass. (I like Stephenson’s explainy-ness! Really, I do.)
[* Julia Bliss Flaherty “JBF” – I felt she was modeled on Hillary Clinton, but a bit younger. Two other characters had pretty clear real-world models: Dr. Doob, astronomer and “science popularizer” = Neil Tyson Degrasse; Sean Probst, .com billionaire turned space startup CEO = Elon Musk/Jeff Bezos.]
Once they finally reach the relative safety of Cleft, there are only eight survivors – all women. Game over for humanity? Not quite … luckily Moira, a certified genetics genius, is one of the eight and evidently reproduction is a piece of cake even with no males involved. Happy day! In about a fifteen minute pow-wow (eh, it’s only the future of humanity, no big deal), the gals decide to each genetically modify their offspring to introduce new traits. (Hmmm… kind of just boosting the population might be in order before you start messing with that stuff, I think. Also, hard to believe that someone didn’t keep on tinkering over the next several thousand years – why are there still only basically seven races after all that time?)
One of the eight is beyond child-bearing years, so that leaves seven progenitors to found their own races: Dinans (heroic), Ivyns (smart), Teclans (strong), Moirans (genetic shape shifters … told ya it was cool that she scored that 0.000000133% chance of being one of humanity’s survivors!), Aidans (sneaky and counterbalanced to each of the others – Aida was the head of the cannibal contingent), Camites (non-aggressive, so as to thrive in cramped space habitats. Lame!) and Julians (manipulative schemers).
Some final observations on technology. Those on the ISS and in the Ark use cell phones, blogs, the internet, “Spacebook” … in 5000 years, they still haven’t gotten to our current state of gadgets, mainly from a choice to focus more on massive space infrastructure, but also from desire to avoid “Tav’s mistake” = wasting time with social media and etc. But, then it is interesting that Blue’s “General” is a media-conscious reporter. Winning battles is not so important as convincing people of the right “narrative.”