This is eighth in a Contemporary Fantasy series and characters and plot carry over from the start. So I definitely recommend reading them in order.
My usual, but non-standard, disclaimer applies here. I do my best to be honest, but part of that is admitting how much I adore Melissa, even after living together over a quarter of a century. If you want to disregard anything I have to say, that's fair enough.
The last couple of books have had the Wardens reacting to the Mercy and this book marks a change in tactic. And that marks a change in tone as well (though a subtle one). It starts with Helena learning more about her ability to see through illusion and some of what that means and how it relates to the Long War. At the same time, the Oracle itself begins taking an active interest in the war, including some preemptive auguries that prompt Helena to act sooner than later in gathering those like her together. And it isn't long before war happens and things get actiony in a way that hasn't been common up until now.
From there, the story enters a non-stop pace with action and reaction and lots of tense developments. I knew what to expect, so I actually took the day off work because I knew I wouldn't be able to concentrate on anything else (which turned out lovely and I may schedule that more actively in future book release dates).
I loved getting to know Helena's people. They're an interesting mix with very different personalities and backgrounds and you can see from the start that getting them pointed in the same direction is a nearly impossible task. I particularly loved the friendship with the prickly Jun and the culmination of it chokes me up, every single time.
Anyway, this story sets us up for the next, and last, to come and does so without ever feeling extra or unnecessary or like it's just filler. The stakes have never been higher and the more we see of the invaders, the creepier and scarier they become. I'm glad this is more action than thriller and can't wait to get to the end!
Some inside baseball: This one is dedicated to the bookstore that put the germ of an idea into Melissa's head. The Arcadian is an amazing bookstore but I'm always torn about whether I mean that negatively or positively. Melissa has two book-related superpowers. The first is that she can enter any bookstore anywhere and come out with at least one unexpected treasure. This was never more amazing than at the Arcadian.
A note about Chaste: Helena and Malcolm are married and intimate. Which means sex. Which is sometimes mentioned. But nothing explicit ever hits the page. So I consider this chaste, but others may reasonably differ.