Lady of the Lake is the last book in the Witcher series by Andrzej Sapkowski. I’ve heard that there’s another book, Season of Storms, which will come out (translated in English) in 2018, but I think that one’s a short story collection.
Ciri escaped the torturing arms of her pursuer, and fled into the Tower of Swallows. It transported her to a world of Elves, but not the Elves she knows. She is a prisoner, and they will only let her go if she agrees to do one thing. One terrible thing. Meanwhile Geralt is looking for Ciri back in their world with his companions, trying to save her from those who wish to harm her, or control her. Yennefer has been put in chains, and tortured, by people who want to get their hands on her surrogate daughter. And the Emperor of Nilfgaard too has his eye on the prize.