Timespell by Ann Gimpel

A druid’s determination…A witch’s stormy rite of passage…
Katerina eats, sleeps, and breathes cultural anthropology. The only stain on her success is her worry she’ll go mad just like a few other women in her family. That fear rockets to the fore when she’s on a lecture tour in the Scottish Highlands and hallucinations grab her, visions rife with horrors straight out of medieval folklore.
Arlen, Arch Druid for all of Great Britain, hasn’t called on his magic much in the past hundred years. No need for it in the midst of the twenty-first century. While attending a lecture, he detects fell forces. A closer look reveals the impossible. He’d thought the Roskelly witches long dead. Brutal, feral, violent, they were the force behind Scotland’s bloodiest clan wars. Risen from their crypts, they’re intent on Katerina. What he can’t figure out is why.
Finally! A challenge for his long-neglected powers. Far from being grateful, though, Katerina doesn’t trust him. Why should she? A headlong dash to escape his unwanted attention lands her three hundred years in the past with no way out.