Ashes of Honor by Seanan McGuire was coming out in early September instead of Mid-September. It was a nice surprise and caused a lost day. It was nice.
Anyway, we rejoin our heroine as she has to prevent a changeling with too much power from accidentally destroying the world by reopening the sealed portions of Faerie. Of course it isn't as simple as that, it never is, the villain is causing arbitrary trouble that could cause terrible things to happen in San Francisco.
I shouldn't say arbitrary, it's more how the villain just doesn't care. The villain wants something to happen and needs assistance, so they make a deal. That deal has ramifications, but the villain isn't considering that, just as they aren't considering the ramifications of opening a sealed portion of Faerie even temporarily.
The most enjoyment of the book though is revisiting old character's who haven't been seen since book two, discovering some of what you expected about characters from small statements they had made, and Quentin finally getting taller than Toby.
Okay, I can't say anymore without giving spoilers (and if you look closely, I already did), so I'll just leave this with a "Go read it".