Luthias by Hazel Hunter

Time travel was not in her job description.

Emery Parker can hardly believe her luck. She’s landed the museum internship of her dreams: working with a collection of ancient Scottish swords. But when she finds herself locked in a stone room of weapons that look brand new, she demands to know what kind of game is being played.
Laird Luthias MacRoss has never believed the legend of the Fire Sword. But the appearance of a young lass in his armory changes his mind. Not only does she possess the delicate beauty of the Fae, she holds their sword in her hand.
But as her purpose slowly becomes clear and their torrid attraction blossoms, Luthias finds he must choose between his heart and the good of his clan.