Gideon the Ninth was excellent. Somehow, I think this one was even better. (Maybe it's the extra tragedy, I do love some good tragedy.) In Gideon, we got Gideon's perspective on Harrow from the outside. In Harrow, [spoilers for Gideon, but not really Harrow]

we got Gideon's perspective on Harrow from the inside

, and it made her much more sympathetic, both getting more of Harrow's story and, well, the main plot of the novel, which just made my heart break for her. And though there's not really any mystery for the reader (though in the end there might be a little bit more than you expect), the way the book is written means the whole book still has a somewhat mysterious feel to it. (Also, this book was somehow even smaller in scope than Gideon, but this was in no way a disappointment.)