Why is Madelaine in danger in the story, Hotel Transylvania?

In the story, Hotel Transylvania, Madelaine de Montalia finds herself in danger from a group of Satanists led by the evil Baron Clotaire de Saint Sebastien because her father, in the waywardness of his youth, had promised his first-born child to the devil-worshippers, and they have never forgotten. Their intent is to make her the subject of a ghastly and painful sacrifice to Satan.