Highlander Unconquered

Ian Stuart trips and falls at a Hogmanay celebration—and opens his eyes to find a beautiful woman straddling him enticingly. She accuses him of putting her there, but he'd definitely remember that. Furthering confusion, she doesn't know where she is or how she got there. Rather than leave her alone in a strange place at night, he takes her home to Kilcoy Castle.
The last "normal" thing Thea Ross remembers is checking whether the fallen man was hurt. Now she's in eighteenth-century Scotland, ...