The Highlander’s Keep by Bess McBride

Cynthia Dunnon, graduate archaeological student, heads off to the remote Western Isles of Scotland to work on a dig of the sixteenth century island stronghold of the Morrison clan. Just as she is packing her bags to leave, her long-time boyfriend ends their relationship, claiming that her love for him lacks passion and romance. Cynthia, the daughter of an absentee irresponsible archaeologist father, wants a steady reliable relationship devoid of drama.
No sooner does Cyn set foot onto the foggy tidal sea stack of the Morrison stronghold than she falls headlong into a deep hole, all that remains of the keep that served as a lookout tower from rival feuding clans. A metal object slows her fall, the hilt of a medieval dagger.
Cyn finds she has fallen not only in space, but in time, when she awakens in a world of rugged Highland Scotsmen who stand ready at all times to fight for their home, their women and children, their very lives. Steady and reliable they may be, but they are fiercely passionate about everything they hold dear.
Cyn finds a sympathetic companion in Ann Borodell, the time traveling wife of the laird. But it is the wild ginger mane and compelling blue eyes of the brooding Highland warrior that capture her reluctant heart.