Grave Peril - The Dresden Files, Book Three

Meet Harry Dresden, Chicago's first (and only) Wizard P. I. Turns out the 'everyday' world is full of strange and magical things - and most of them don't play well with humans. That's where Harry comes in. Harry has faced some terrifying foes during his career. Giant scorpions. Oversexed vampires. Psychotic werewolves. It comes with the territory when you're the only wizard in town. But in all Harry's years of supernatural sleuthing, he's never faced anything like this: the spirit world's gone loco.
All over town, ghosts are causing trouble - and not the door-slamming, boo-shouting variety. These ghosts are tormented, violent, and deadly. Someone is stirring them up to wreak havoc. But why? And why do so many of the victims have ties to Harry? If Harry doesn't figure it out soon, he might just wind up a ghost himself. Magic - it can get a guy killed.