A Court of Silver Flames (A Court of Thorns and Roses Book 5) by Sarah J. Maas

Nesta Archeron has always been prickly, -proud, swift to anger, and slow to forgive.the person who ignites her temper more than any other is Cassian, the battle-scarred, winged warrior who is there at Nesta’s every turn. As the threat of war cast its shadow over them once again, Nesta and Cassian must battle monsters from within and without as they search for acceptance-and healing-in each other’s arms.

The one person who ignites her temper more than any other is Cassian, the battle-scarred warrior whose position in Rhysand and Feyre's Night Court keeps him constantly in Nesta's orbit. But her temper isn't the only thing Cassian ignites. The fire between them is undeniable, and only burns hotter as they are forced into close quarters with each other.

Meanwhile, the treacherous human queens who returned to the Continent during the last war have forged a dangerous new alliance, threatening the fragile peace that has settled over the realms. And the key to halting them might very well rely on Cassian and Nesta facing their haunting pasts.