This is Book 4 of the Dresden Files.
I have said that these books keep getting better. This is the best one yet.
The political consequences at the end of Book 3 set the scene for the turmoil at the start of Book 4. Harry is in deep, hemmed in from all sides by the White Council, the Red Court, the Winter Lady, missing persons, and a whole list of people (dead, alive, and otherwise) who are trying to get him killed.
There is a lot going on in this book. It gets pretty busy in the middle and timelines are a little fuzzy, but in all it turns out to be a great political chess game where the answers aren't revealed until the very end. There are plenty of surprises here, and you are given the very first glimpse into the inner workings of the White Council.
Some of the issues are resolved in one way or another, but other issues remain open-ended and will hopefully be addressed in the coming books. Butcher is building an incredible world here and he is making each new adventure well worth the ride.