The Lady in the Castle. The Scottish Lady, #1

Alanna Ferguson would be her grandfather's heir when he passed on, and so she dutifully applied herself to her responsibilities at Castle Ferst and the surrounding land and towns in northern Scotland. When American Nathan Hunter arrived to find out why his company's oil survey work had been shut down he found it in the form of the independent minded young redheaded girl in the castle. Their first meeting goes poorly, but he finds himself fascinated with the castle, and with the dungeons below, and soon realizes Alanna has had a life-long fascination of her own with the cold stone cells and their dark history.
When he almost playfully slips shackles around her wrists, though he discovers just what heat that fascination could produce as heir own dark fantasies take control of them.