The premise is that Harry Dresden has found himself at ground zero of the biggest supernatural war in centuries, if not millennium. The Last Titan, Ethniu, has returned at the head of an army of Formor that have removed themselves from the Unseelie Accords. Faced with the revelation of the supernatural to humanity and total war, the remaining Unseelie Accord nations band together for a fight that will end with one side destroyed.
The book is essentially one enormous Saving Private Ryan-esque war movie. Harry does battle with kraken, hordes of Formor goons, mutated children, Black Court vampires, and the Titan herself in his efforts to save the millions of citizens living in Chicago. Along the way, Harry will be forced to confront numerous old foes as well as deal with the fact he's burned a lot of bridges with former allies that he didn't even bother to inform he was still alive past the events of Changes.
Jim Butcher manages to establish some amazing twists in this volume as well as answer some longstanding questions about the franchise as a whole. A familiarity with Peace Talks is healthy not just because of the fact that events here are a direct sequel but there's a lot of foreshadowing in that volume for plot developments here. A number of things I guessed were foreshadowed events in Peace Talks turned out to happen in Battle Ground. For example, we get the delightfully creepy answer to why Thomas did the horrible thing he did and I am pleased by the result.
Jim Butcher doesn't spare the cast from casualties and several characters that have been long parts of the series are struck down during this event. I was really stunned at a couple of the fallen and think they were handled with great dignity. This is one of the most devastating battles of Harry's career and I give Jim props for having the courage to go the direction he did. Military fiction with no casualties on the good guys' side isn't heroic, it's just silly.
There are a few flaws in this book, I admit. I think this really would have been better as one enormous volume because a lot of the story in Peace Talks flows directly in this volume. I also believe that there were a few "random encounters" that didn't add much to the book. I think they could have been eliminated without interrupting the narrative much. None of them are boring, though, and many of them are quite entertaining. I just felt that a superpacked Peace Talks/Battle Ground would have been a stronger story.
The politics at the end of Battle Ground also strike me as something I wish the books had gotten into. I was hoping Peace Talks would get into the subtle and not so subtle court bickerings of the Unseelie Accord Nations. Mab proves to be an expert politician in forging alliances, some including some really surprising ones, with a few shocks that I actually approve of. I also note the White Council continues to be a bunch of jerks. Their decision makes sense but also shows a fantastic lack of gratitude that is entirely consistent with their previous behavior.
In conclusion, Battle Ground is a really solid piece of writing. It is full of non-stop action from beginning to end but isn't hurt for characterization in the process. While I think the book suffered from being split from Peace Talks. Still, anyone who was disappointed on the lack of payoff in that book will be blown away by all of the results from actions taken here. If you're a fan of the books then this will surely be one of your favorites--unless one of the deaths breaks you.