Throne of glass by Maas, Sarah J.

‘Throne of Glass’ begins the sweeping saga of assassin Celaena Sardothien, who is serving a life sentence in the mines of Endovier – until a young captain of the guard offers her a deal. She will have her freedom, on one condition: she must fight to win a deadly competition to serve as the champion of the king. The king who rules his kingdom with a cruel and merciless hand. Live or die, Celaena will be free. Win or lose, her destiny will claim her.