This is a part of the Discworld series, featuring the Lancre witches and a family of Vampires. Magrat and Verence are getting married, and Verence invited the vampires to Lancre as a part of the celebrations. They begin taking control of people’s minds and as such the town itself.
This one is pretty excellent I think, Granny Wetherwax is on fine form and the scenes between her and the Omnian priest Mightily Oats are wonderful. The whole book is I think about frustrations with moral relativism. Both inaction in the face of despicable behavious, and the justifications used to support them.