*Surprises and spoilers contained within...*
It's a story about a ghost.
The ghost of Harry Dresden.
You thought he would survive the assassin's bullet, didn't you?
You thought because he'd beaten the loup-garou and the skinwalker, battled the legions of heaven and hell, walked the paths of the Nevernever, annihilated the entire Red Court with a single spell, backtalked/sassed/gave lip and generally pissed off gods, goddesses, wizards, creepy little girls with vast amounts of knowledge, FBI agents, necromancers, the entire Chicago police department, hellhounds, mob bosses, queens, knights, priests, fairy godmothers, werewolves, medical examiners, wardens, valkyries, tv show hosts, enforcers, ectomancers, pub owners, and homicidal ex-girlfriends that he was somehow invincible?
Yeah. Me too.
"Here Lies Harry Dresden. He Died Doing the Right Thing."
But a wizard's work is never done, not even after death. Harry couldn't get that lucky. After death, things really start to get interesting. That's part of Harry's curse; he lives (and dies, apparently) in interesting times.
I thought it would be impossible to top Changes, the previous novel in the Dresden Files series; it was just that good. So Jim Butcher didn't try. Instead of throwing punches and fists full of fire (Fuego!) to beat his last book, Butcher bobbed, he weaved, he faded out to the incorporeal. Topping Changes became a non-issue. A moot point. A ghost.
"He dodged it," as my friend and fellow Dresden fan, Clint, so aptly put it.
He went in a totally different direction.
In order to get the most out of Ghost Story, I highly recommend reading Side Jobs, the collection of Dresden short stories published between Changes and Ghost Story. The last chapter, Aftermath, helps explain the developments since Harry's death and the appearance of the Formor. It's not a must, but it definitely clarifies a few things and sets up Ghost Story nicely. Plus the short stories are good, clean (except for "Love Hurts", but it's a good kind of naughty) fun.
In Ghost Story, readers learn more about characters introduced in earlier novels, meet a few new characters, and explore the wounded depths of Harry's friends and frenemies after his death. Harry realizes the enormous impact his life, death, and afterlife has had on everyone around him, as well as the city that he calls home.
Harry may be dead, but don't write him off yet. It ain't over 'til the valkyrie sings.