I've no spoilers of Familiar Magic in this review but if you haven't read Underground Magic, the series' excellent prequel, stop right here and go read that. You can get it from the author for free and it's worth the read. Warning though: by necessity this review is a major spoiler of Underground Magic.
This book started off with a gut punch. I'd read Underground Magic and was really looking forward to seeing further interactions between Kala, Trin, & Feal, the three most powerful witches of London, and their newly created familiar Stella Familiar (yes, I've said this before: gotta love that name). Then on page 1 of this book (so not really a spoiler of this book) all three of the witches are found murdered! Humph. (I'd still recommend Underground Magic though as it's s well written back story and great as a stave-alone novel.)
It's really fun following Stella in action as she gets revenge on what killed her creator (see, I'm being careful here: no spoiler-ish hints about what that is). A mystery and a thriller, full of magic and adventure in a really wonderfully thought out plot. An extraordinarily well drawn lead, supported by a wonderful cast of supporting characters and, yes, a final resolution that's fully satisfying while still leaving me salivating for the next book. This was pure fun and highly recommended.