The House by Exmoor — Caroline Stafford

Pretty and penniless Alexandra Townsend thought the job of companion to Theresa Andover, a rich young invalid, would be ideal. But from the moment she arrived at Twelve Oaks she was treated like an intruder. Theresa completely ignored her presence - until Sir Richard, the domineering master of the mansion, came home again. -- As soon as Sir Richard met Alex he dismissed her as too inexperienced to deal with his cold and calculating sister-in-law, Theresa. But Theresa suddenly insisted that Alex must stay on.

Alex decided to remain at Twelve Oaks. She found herself strangely attracted to the darkly handsome Sir Richard. And she quickly realized that he had been trying to protect her from something, something powerful and menacing....