Christmas in a Castle by Samantha Hastings

Miss Mary Perkins is governess to the strong-willed Stringham sisters while waiting for her beloved Mr. Trevor Wallace, a curate, to receive a living so that they can afford to marry. When he loses the promised position, her young charges decide to give their governess a husband for Christmas. The Stringham sisters write a fake letter from the duke inviting Trevor to stay at the castle, lock the pair in the dungeon, accidentally poison a chaplain, and cause a great deal of mayhem with mistletoe. Despite the girls’ well-meaning mistakes, will Mary and Trevor finally have the wedding of their dreams?