In many ways, Nona is like other people. She lives with her family, has a job at her local school, and loves walks on the beach and meeting new dogs. But Nona is not like other people. Six months ago she woke up in a stranger's body, and she's afraid she might have to give it back. The whole city is falling to pieces. A monstrous blue sphere hangs on the horizon, ready to tear the planet apart. Blood of Eden forces have surrounded the last Cohort facility and wait for the Emperor Undying to come calling. Their leaders want Nona to be the weapon that will save them from the Nine Houses. Nona would prefer to live an ordinary life with the people she loves, with Pyrrha and Camilla and Palamedes, but she also knows that nothing lasts forever. And each night, Nona dreams of a woman with a skull-painted face.

Harrowhark Nonagesimus, last necromancer of the Ninth House, has been drafted by her Emperor to fight an unwinnable war. Side by side with a detested rival, Harrow must perfect her skills and become an angel of undeath --- but her health is failing, her sword makes her nauseous, and even her mind is threatening to betray her. Sealed in the gothic gloom of the Emperor's Mithraeum with three unfriendly teachers, hunted by the mad ghost of a murdered planet, Harrow must confront two unwelcome questions: Is somebody trying to kill her? And if they succeeded, would the universe be better off?

Brought up by unfriendly, ossifying nuns, ancient retainers and countless skeletons, Gideon is ready to abandon a life of servitude and an afterlife as a reanimated corpse. But her childhood nemesis won’t set her free without a service. Harrowhark Nonagesimus, Reverend Daughter of the Ninth House and bone witch extraordinaire, has been summoned into action. The Emperor has invited the heirs to each of his loyal Houses to a deadly trial of wits and skill. If Harrowhark succeeds, she will become an immortal, all-powerful servant of the Resurrection. But no necromancer can ascend without their cavalier. Without Gideon’s sword, Harrow will fail, and the Ninth House will die. Of course, some things are better left dead.