The Valcourt Heiress by Catherine Coulter

The Valcourt Heiress - Merry’s father has suddenly died.  Her mother, Abbess Helen of Meizerling Abbey, has returned to marry her off, rather sell her to Jason of Brennan; a man that Merry is sure is evil.  Merry tries to run away but Sir Halric, Jason’s man, capture’s her and tries to take her back to his master.  Garron of Kersey is on his way to Wareham Castle to claim his title when he meets Halric just as Merry is fighting to escape.  When he gets home he finds that the Black Demon has killed most of his people and destroyed the castle.  Merry finds her way there and takes over the remaining servants and gets the castle in shape.  Helen, who has the reputation of being a witch, kidnaps Merry to force her to marry Jason once he finds the silver coins that are suppose to be buried at Wareham castle.