As with the first book, I found this one improved as it approached the climax, with several clever uses of the magic available to the protagonists. The characters are a little overwhelmed by the plot in this book: it's a big world-and-history-spanning epic, with lots of ramifactions that reverbate through the narrative.I do like the way the series started as a "secret magic" setting, and is evolving into "secret exploded, everybody knows" instead.
Isaac has been ground down by the events of the last two books, but still gets some delightfully geeky moments. The polyamory angle is handled well, with maturity and commitment on the part of the participants, and obvious imperfections that they deal with. There were some weaknesses in the book, but overall I enjoyed it and am looking forward to the series' conclusion, coming out in February! (I will note that the book has a solid conclusion:it resolves the central conflict decisively. No cliffhangers!) I'll give it an 8.5.