Seveneves recap

The Moon inexplicably shatters, and scientists determine that its fragments will soon collide in a cascade that will burn Earth's surface for thousands of years. Humanity expands the International Space Station into the Cloud Ark while people on the ground create other survival projects. When the Hard Rain begins, the orbital refuge is damaged and divided by politics. A breakaway swarm led by former president Julia Flaherty suffers catastrophic losses, and the remaining survivors seek shelter in a fragment of the Moon. Only seven women remain able to found future generations: Dinah, Ivy, Julia, Moira, Camila, Tekla, and Aïda. Five thousand years later their engineered descendants form seven recognizable lineages and inhabit vast orbital structures while restoring Earth. An expedition led in part by Kath Two discovers that underground and underwater groups also survived the catastrophe. Humanity's future therefore rests on the reunion of three civilizations, not solely on the legacy of the seven women in orbit.

The Moon breaks into seven large pieces without warning and for no known reason. At first the fragments remain in orbit, but astronomer Dubois Harris concludes that repeated collisions will produce an exponential cloud of debris. Within about two years, pieces will begin entering Earth's atmosphere in a sustained bombardment called the Hard Rain, heating and devastating the surface. Governments accept that almost everyone on Earth will die. The International Space Station becomes the center of an emergency plan: it will be enlarged with many small arklets, populated by young representatives selected from around the world, and supplied with genetic material and technical knowledge. Roboticist Dinah MacQuarie and station commander Ivy Xiao begin adapting the station, while Dubois returns to Earth to explain the danger publicly and assist the planning effort.

Humanity spends its remaining time building the Cloud Ark and pursuing scattered alternatives. Geneticist Moira Crewe prepares an archive that could support future generations. Dinah develops robots and structural systems for work around the station. Mining entrepreneur Sean Probst seeks useful material beyond Earth, while Dubois calculates how the changing lunar debris will affect possible refuges. Political arguments persist over who will go and who will control the survivors. Thousands of arklets assemble near the station, each carrying a small national delegation but depending on a shared command and infrastructure. President Julia Bliss Flaherty reaches orbit shortly before the end, bringing political authority into a community organized around technical command. On Earth, people complete what shelter projects they can and say farewell as the sky begins to change.

The Hard Rain destroys the surface and kills the people left on Earth. In orbit, the ark community survives the first catastrophe but remains exposed to debris, radiation, hunger, and failing machinery. The large, loosely connected population becomes harder to govern. Julia challenges the command structure and encourages many arklets to form a separate swarm, arguing that dispersal gives them a better chance than remaining near the station. The split sacrifices shared resources and creates two rival plans for survival. Accidents and collisions reduce the population, and the breakaway group suffers heavily as its members attempt to move without enough propulsion, supplies, or experience. Those remaining with the station pursue a hazardous route toward a large surviving lunar fragment that might shield them from the debris environment.

The survivors' effort to reach lunar shelter costs more lives and leaves the original Cloud Ark drastically reduced. The separated swarm returns in desperate condition, its members divided and traumatized by starvation. Violence follows the reunion, and only a handful of women remain when the survivors finally secure a refuge inside the lunar remnant. Dinah, Ivy, Julia, Moira, Camila, Tekla, and Aïda become the Seven Eves from whom a new population can be created. Moira explains that she can use the preserved genetic archive and limited adjustments to prevent immediate inbreeding, but each woman also chooses traits she wants emphasized in her own descendants. Their personal and political differences will therefore persist as biological lineages. The first age of the story ends with humanity reduced to this small founding group and its stored inheritance.

Five thousand years later, the descendants of the Seven Eves number in the billions. Their seven broad lineages retain traits associated with the founders and have developed distinct cultural and political identities. They live in enormous orbital habitats, including a ring around Earth, and have begun making the planet habitable again. Kath Two, a young descendant of Dinah, is drawn into a secretive expedition after signs suggest that people may be living on or near the recovering surface. The mission brings together members of several lineages and forces them to work across the old divisions. Their investigation encounters evidence of humans whose history does not descend from the seven orbital founders.

Kath Two's expedition confirms that the Seven Eves were not the only ancestors of living humanity. One population, known as the Diggers, descends from people who survived the Hard Rain in deep underground works connected to Dinah's father, Rufus MacQuarie. Another, the Pingers, descends from a community that survived beneath the oceans and adapted over thousands of years to an aquatic environment. Representatives of the three branches meet as the orbital civilization continues restoring Earth. The encounter overturns the founding story on which the seven orbital races built their identities. No complete political settlement is reached; instead, the survivors' descendants face the task of recognizing two human civilizations formed without them. The same problem that governed the Cloud Ark now returns on a larger scale: technically advanced groups with different histories must choose whether cooperation can overcome fear, rivalry, and inherited assumptions.

Five thousand years after the Hard Rain, the descendants of the seven surviving women have rebuilt humanity in orbital habitats and begun to terraform the damaged Earth. Kath Two joins a mission that uncovers two other human populations. The Diggers descend from people who survived underground, including members of Rufus MacQuarie's mining community; the Pingers descend from people who adapted to life beneath the sea. Both groups have developed outside the assumptions and politics of the seven orbital races. The expedition makes direct contact with representatives of these populations, turning the old belief that only the Seven Eves preserved humanity into an incomplete history. The novel closes at the beginning of a difficult reunion among three branches of humankind rather than with that reunion settled: orbital civilization has great power, but it must now decide whether it can meet its terrestrial cousins without repeating the factional errors that nearly destroyed the original survivors.