Nona the Ninth continues from Harrow in featuring a character who is continuous to Harrowhawk Nonagesimus from the first book, but also very much not the same person. While Harrow from book 2 deliberately edited her memory to avoid eating Gideon Nav's soul, Nona is a child in the same body. She's been alive for about six months, living an underground childhood in a city outside the control of the Houses, but very much not under control.

Nona is an inexperienced and partial narrator, but I loved seeing what life was like for ordinary people in this setting. And the answer is, mostly very awful. The Houses necromancy takes an irreversible toll on planetary biospheres. This takes centuries, but on a social timescale, centuries are not actually all that long. Ordinary people have been shuffled from resettlement to resettlement, perennial traumatized refugees seeking solace in the bloody answers of the anti-necromancy resistance group Blood of Eden. The low-level civil war on Nona's new home is going towards high-level, because a Resurrection Beast has it's awful gaze on the planet, and the forces of the Empire are going to show up to Do Something About That, whatever the locals want.

A third of the book is Nona's cozy domesticity, living with Pyrrha Dve and Camilla/Palamedes, going to a local school and being friends with an unlikely gang of tough survivor kids. Another third is interludes from the past, John Gaius reminiscing about how he became the Necrolord Prime, the bad old days when he was just a late 21st century scientist trying to figure out how to save everybody on a dying Earth. His plan involved cryogenic suspension and FTL evacuation, against the suspicious that a bunch of trillionaires were planning to get themselves off-planet and leave everyone else to die. John is a monster, but he's also just this guy, you know. Someone facing impossible circumstances with bad options. Is necessity an excuse? Is it possible to find forgiveness in immortality?

And the last third of the book is high octane intrigue, swordfights, and necromancy, as Ianthe the First, a revenant of Gideon Nav, now claimed as Prince of the Empire and Heir to God, the Blood of Eden, Nona, and everybody collide on the Locked Tomb, seeking the power that made necromancy possible.

On this plus, as always Muir is a master of tone and style. On the minus, this series is getting pantsed as hell, and I'm not sure if it's incredibly clever or incredibly lucky. The thing is that I know Muir is very very good at short fiction. The appendix material in both this book and Harrow are better than the book itself. Undercover was one of the best things I've read. But I'm not sure you can build a marathon out of linked sprints.