Warrior Witch By Danielle L. Jensen

The epic conclusion to YA romantic fantasy trilogy from the USA Today bestselling author of Dark Shores and The Bridge Kingdom!
Cécile and Tristan have accomplished the impossible, but their greatest challenge defeating the evil they have unleashed upon the world.
As they scramble for a way to protect the people of the Isle and liberate the trolls from their tyrant king, Cécile and Tristan must battle those who’d see them dead. To win, they will risk everything. And everyone.
But it might not be enough. Both Cécile and Tristan have debts, and they will be forced to pay them at a cost far greater than they had ever imagined.
Reading 1) Stolen Songbird 2) Hidden Huntress 3) Warrior Witch 4) The Broken Ones (prequel)