The main plot of this book is that something is disrupting the boundaries between the spirit world (The 'nevernever') and the real world, letting all kinds of dead things come through. As usual, there is a hell of a lot going on, but as usual Butcher manages to coordinate it all very well. The thing I really like about these books is that because he uses very understandable laws of magic, the mystery element of things works very well. The ultimate 'who dun it' in both cases follows a logical pattern.
And yet the thing that I really like about this series is that while there is a formula, by the end of the book Butcher takes that formula, crumples it up in a tiny tin foil ball and tosses it out the fiftieth story window to make a nice impact on the concrete below. Harry's actions have consequences, and I LIKE consequences because consequences are what happens when a character matters.
Its why I stopped reading comics except in graphic novel form, because no one stays dead, and another writer can completely undo anything that the previous writer has done. Now, it is true that in the real world change always happens and nothing ever lasts, but then again, in the real world, people stay dead. In fact, in all of the books I've read so far by Butcher, dead people have stayed dead, which given a world in which time travel is theoretically possible (its one of the laws of Magic not to muck around with time) in either the Dresden books or the Codex Alera books I have yet to see him bring someone back to life....it might happen, but it certainly won't be the revolving door it is in a lot of series.
(Note: Obviously vampires and ghosts are back from the dead, but they stay that way.)