Reached recap

Cassia is back in the Society as a sorter, trading forbidden poems with the Archivists; Ky flies for the Rising; and Xander, a physic, has been a member of the rebellion for years. The Rising makes its move by releasing a plague that leaves its victims motionless, then offering the cure it has been holding all along, and the Society collapses within days. The takeover unravels when the plague mutates and the cure stops working, leaving thousands of people still and unwaking, including people all three of them love. Ky falls ill. Xander leaves the cities for a village beyond the Rising's control, where an old man who worked on the original cure builds a remedy from a plant the villages preserved, and the three of them get it distributed largely without the rebellion's permission. In the process it becomes clear that the Rising engineered the plague, planned the takeover and intended to keep deciding for everyone. With both regimes discredited, the future is put to a vote, and Cassia and Ky end the trilogy together and free to choose.

Previously: in the Society, data decided what citizens ate, whom they married and the day they died. Cassia Reyes was Matched with her friend Xander, then saw Ky Markham's face flicker onto her official microcard, and fell in love with a boy classed as an Aberration who could never be Matched. Her grandfather, killed on schedule at eighty, left her two poems the Society had destroyed everywhere else. Ky taught her to write by hand and told her the history the Society had erased, including a father who died for the rebellion. When Officials noticed, Ky was sent to the Outer Provinces as an expendable decoy and Cassia's family was demoted; Cassia rigged her own records to be sent to a nearby work camp. Both escaped into the canyons, survived the crossing, and reached the Rising, which accepted them and split them up: Ky and Indie to fly, Cassia back into the Society as a sorter. Cassia also learned that Xander had been a member of the Rising for years without her knowing.

The book is told by three narrators. Cassia sorts data in the central city and waits for the Rising's signal, trading poems with the Archivists and quietly gathering the writing and art that ordinary people make for themselves. Ky flies transport runs for the rebellion, still unconvinced by it. Xander works as a physic inside the Society's medical service and has believed in the Rising far longer than either of them; the inoculations he has been giving citizens are part of a plan he has not been shown in full. Then people begin falling ill, everywhere at once, and stop moving.

The plague spreads faster than the Society can hide it. Victims are not killed but immobilized, breathing and alive and entirely unresponsive, and there are soon too many of them for the medical centres to hold. Within days the Society's authority collapses, because a system that promised to have calculated everything cannot explain this. The Rising steps into the gap with the one thing nobody else has: a cure. It takes over the cities, sets up treatment centres, and presents itself as the rescue rather than the cause.

With the Rising in charge, the three of them find themselves in the same city for the first time in a long while, and Cassia and Ky are able to see each other again. The rebellion keeps working, and the cure keeps working, until it does not. New patients begin arriving who do not respond to treatment at all: the plague has mutated, and the cure the Rising built its whole takeover on has no effect on the new strain. The number of still patients climbs, and nobody wakes.

The Rising's competence and its honesty both come into question as the wards fill up. Information is restricted, official statements stop matching what the physics can see, and Xander realizes that his own certainty about the rebellion was built on being told only what he needed to know. Cassia works on the problem from the sorting side, looking for a pattern in who falls ill and who does not, while the city's ordinary people, cut loose from both the Society's routines and the Rising's promises, start writing, painting and trading words in public.

Ky falls ill with the mutated strain, which turns the crisis into something immediate for all three narrators. Xander leaves the cities for the settlements beyond them, following the one lead worth following: an old man named Oker, who worked on the original cure long before the Rising had any use for it, and who is difficult, exacting and unwilling to be owned by anybody. In the villages Xander also meets Lei, and finds a way of practising medicine that owes nothing to either regime.

Oker builds a remedy for the mutated strain out of a plant the villages have preserved and a method the Society spent generations trying to erase, with Xander and the settlements doing the work of testing and preparing it. Getting it to the sick is a separate fight: the Rising wants control of it, distribution and credit alike, and would rather move slowly and correctly than let anyone hand out a cure it does not administer. Cassia, the Archivists and the villagers begin moving it themselves.

The remedy reaches the wards and the still begin to wake, Ky among them. What the epidemic has exposed cannot be walked back: the Rising engineered the plague, held the cure, timed the collapse and always intended to govern afterwards on the same terms the Society used, deciding what people should know and what they should be allowed to choose. Ky's long refusal to trust it turns out to have been accurate. The Pilot and the rebellion's leadership are left arguing their case in public rather than issuing it, while the villages and the Archivists hold the one thing everyone needs.

With both the Society and the Rising discredited, the question of who should govern is left genuinely open, and it is settled by putting it to the people to decide for themselves, the first real choice anyone in this world has been given. Cassia and Ky come through the crisis together and are no longer at anyone's disposal; Xander, whose faith in the Rising was broken by what he learned, finds his own footing in medicine and with Lei. The words, paintings and handwriting that ordinary people produced in the middle of the epidemic are kept rather than sorted away, and the trilogy ends with the future uncertain and, for the first time, chosen rather than calculated.

The remedy that works against the mutated strain is made outside the Rising's control, from a plant and a method preserved by people the Society had spent generations trying to erase, and it reaches the sick largely because Cassia, Ky, Xander and the villages distribute it themselves rather than waiting for permission. The still begin to wake. What the epidemic exposes is that the Rising was never the opposite of the Society: it engineered the plague, kept the cure, planned the takeover in advance, and its leadership fully intended to go on deciding for everyone afterwards, which is the conclusion Ky reached about it long before anyone would listen. With both the Society and the Rising discredited, the question of who governs is left open, and it is answered by putting it to the people to choose for themselves, the first genuine choice anyone in this world has been offered. Cassia and Ky end the trilogy together and no longer at anyone's disposal. Xander, who gave the Rising his faith and had it broken, finds his own footing in medicine and with Lei. The cities keep the poems, the paintings and the handwriting that people made in the middle of the crisis, and the future is uncertain in a way none of the characters mind.