I blazed through this book after re-reading Gideon and Harrow (and I'm glad I did- there were details there that were great to have been reminded of). Overall this was a great story; Nona is an interesting mystery and trying to figure her out is part of the fun of this book. It does start off a bit slow, but towards the end it is rushing and almost too much is going on to fully follow it all. This is one I will have to re-read when the next (yes there is a fourth) book comes out.
For a full review, check out my blog: strakul.blogspot.com/2022/09/book-review-nona-ninth-by-tamsyn-muir.html