Carpe Jugulum by Terry Pratchett

"Mightily Oats has not picked a good time to be priest. He thought he'd come to Lancre for a simple ceremony. Now he's caught up in a war between vampires and witches. There's Young Agnes, who is really in two minds about everything - Magrat, who is trying to combine witchcraft and nappies, Nanny Ogg...and Granny Weatherwax, who is big trouble. And the vampires are intelligent. They've got style and fancy waistcoats. They're out of the casket and want a bite of the future. Mightily Oats knows he has a prayer, but he wishes he had an axe. "Carpe Jugulum" is Terry Pratchett's twenty-third "Discworld" novel - but the first to star vampires."