Empire of Storms Book by Sarah J. Maas

The long path to the throne has only just begun for Aelin Galathynius as war looms on the horizon. Loyalties have been broken and bought, friends have been lost and gained, and those who possess magic find themselves at odds with those who don't.

With her heart sworn to the warrior-prince by her side, and her fealty pledged to the people she is determined to save, Aelin will delve into the depths of her power to protect those she loves. But as monsters emerge from the horrors of the past, and dark forces become poised to claim her world, the only chance for salvation will lie in a desperate quest that may mark the end of everything Aelin holds dear.