Queen of Shadows (Throne of Glass #4) by Sarah J. Maas
Celaena Sardothien is cloaked in her assassin's hood once more. She is back in Rifthold, but this time she is no one's slave. She must delve into her most painful memories and fight for her survival, while resisting a smouldering passion that might very well consume her heart. And she will face her former master, the King of Assassins, again - to wreak revenge for a decade of pain...