Magic Slays by Ilona Andrews

One of the things I like about the Kate Daniels series is that Andrews likes to weave old and forgotten mythologies into the story. In the last book, Magic Bleeds, she used Babylonian references, and in Magic Slays, we encounter some figures from Russian folklore, like Chernebog and Baba Yaga. Just a nice reminder for me of some of the stories I used to read, in Bullfinch's and other sources (For some reason, the title "Albanian Wonder Tales" comes to mind).

Kate's fledgling PI agency is definitely not doing well when she gets a visit from a
member of the Red Guard who offers her a job. Kate can't very well turn it down without having to go to her mate, Curran, for another loan from the Pack to keep things afloat, so against her better judgement - does she have any better judgement? - she takes the case. Her old friend from the Order, Andrea, who disappeared for a long span after she lost control of her were side during the battle with Erra in Magic Bleeds, is back on the scene, and Kate brings her on board the agency to help out. Andrea was thrown out of the Order for not being fully human, broke up with Rafael the bouda, and really has nowhere else constructive to go anyway, so she agrees to help.

It turns out that a squad of the Red Guard were supposed to guard an inventor, Kamen,
while he worked in secret on a device that sucks the magic out of a given geographical
area. The net effect is that all of the humans and other beings that rely on magic to
survive when tech is "down" will die immediately. In a city the size of Atlanta, this would be a major catastrophe, as well as being a bit of inconvenience to Kate and her friends.

Kate discovers some new relatives, and gets back a little bit of her forgotten past. She manages not to do anything too stupid in her relationship with Curran. In the end, an unprecedented gathering of all of the disparate magical groups in Atlanta is required
to solve the issue.

A new group that Kate becomes aware of in this book is a group of "human only" terrorists, The Keepers, whose goal is to rid the world of all magic and magical creatures, thus assuring themselves of power and happiness. Might be some sort of political commentary here about xenophobia or white supremacy, but it's not laid on too thickly. I'm fairly certain we'll see more of this group in the future, as Kate continues to have new adventures.