Death Masks by Jim Butcher

In this book Harry Dresden finds himself up against the vampires (a vampire of the Red Court challenges him to a duel) while he's called on to find the Shroud of Turin which has been stolen from a church in Italy and which seems to be on its way to Chicago. I think the key point of this novel was when one of the spirits that Harry has summoned asks him--why do you do it? He doesn't really have an answer to hand, and I'm hoping that in future books he'll explore his motivations more.