Kingdom of Ash (Throne of Glass #7)

Aelin Galathynius has vowed to save her people ― but at a tremendous cost. Locked within an iron coffin by the Queen of the Fae, Aelin must draw upon her fiery will as she endures months of torture. The knowledge that yielding to Maeve will doom those she loves keeps her from breaking, but her resolve is unraveling with each passing day…

Kingdom of Ash is book number 7 in the Throne of Glass series by Sarah J. Maas.