Legacy of Orisha #3: Children of Anguish and Anarchy book by Tomi Adeyemi

When Zélie seized the royal palace that fateful night, she thought her battles had come to an end. The monarchy had finally fallen. The maji had risen again. Zélie never expected to find herself locked in a cage and trapped on a foreign ship. Now warriors with iron skulls traffic her and her people across the seas, far from their homeland. Then everything changes when Zélie meets King Baldyr, her true captor, the ruler of the Skulls, and the man who has ravaged entire civilizations to find her. Baldyr's quest to harness Zélie's strength sends Zélie, Amari, and Tzain searching for allies in unknown lands. But as Baldyr closes in, catastrophe charges Orïsha's shores. It will take everything Zélie has to face her final enemy and save her people before the Skulls annihilate them for good.