Three Dark Crowns
Arsinoe, Katharine, and Mirabella are triplets who live on an island, raised separately and virtually imprisoned, until they come of age to ascend the throne. Only one of them can do so. Each sister is supposed to have a magical talent. Katharine is a poisoner. Arsinoe is a naturalist. Mirabella is an elemental. The victor must kill her two sisters.

The separate tribes are fascinating. The poisoners are cruel and dark-hearted. The naturalists have familiars/animals they bond with. Elementals control the weather. Mirabella lives with priestesses who are far crueler than the poisoners and who plan to cheat to get Mirabella the crown.

The three sisters were raised together as children, which makes the narrative all the more tense and poignant. The other characters--a brave naturalist girl who is like Arsinoe's sister, Mirabella's priestesses, Katharine's wicked clan, and three interesting young men, (one of whom has a dangerous agenda,)-- make this an extremely enjoyable, if dark, epic fantasy.