Book One of the 'Isavalta' Trilogy, an exciting new fantasy trilogy from US author Sarah Zettel.
Bridget Lederle is the lighthouse keeper of Sand Island Lighthouse, a woman ostracised by the locals because of the bastard child she bore to a visiting Finnish fisherman, and because of her own mysterious antecedents. It is rumoured she's a witch; certainly, she has strange and uncontrollable visions and premonitions.
One day, she has a premonition of disaster and "sees" a small boat being dashed to pieces on the rocks off the island in a storm. The next day the storm kicks up - and she goes out to find a man thrown up on the shore, almost dead. When he speaks, it is in an unknown language; he has bizarre tattoos, and when he wraps a piece of braided cloth about her arm she is suddenly able to understand him.
He tells her he is from another world, a world in which she is a great magical force, and that her presence is required to save the Dowager Empress, currently under threat from her poisonous daughter-in-law. It is an attractive offer for a woman with nothing to lose (her baby died, she has no prospects in our world); she goes with the wizard to Isavalta. But there she will find nothing is quite as he promised her . . .