It took me a while to read this. I didn't realize until the end that it is setting up a series, which explains why the end was rushed and full of twists after a slower-paced, world-building beginning. The last sentence does leave me curious about what will happen next. This was a dark, grisly fairy tale with shades of the dystopian "people fight to the death" and "different groups all think they are the best." Some of the touches (view spoiler)[(the low magic, the sisters, the bears, the island setting), (hide spoiler)] reminded me of my favorite author, Margo Lanagan. 
 The Booklist review sums it up well: "*Starred Review* "Three Black Witches, all fair to be seen / Two to devour, / And one to be queen." So goes a children's song on the mainland, where the natives cast a suspicious eye to the island of Fennbirn. There several strains of magic run strong, and every generation a set of girl triplets is born to the queen. Each has a different magical ability, and they are separated and raised by a family with matching abilities. When they reach 16, their deadly fight for the crown begins, and the last girl standing becomes the queen until her own set of triplets are born. This year, with the triplets' sixteenth birthday approaching, the clear favorite is Mirabella, a powerful elemental who can manipulate the weather. Her sisters--Katharine, who can make and ingest poisons, and Arsinoe, a naturalist who controls plants and animals--are weak, their powers barely manifested. The outcome of the fight should be obvious, but there are other forces at work here, and the battle is only just beginning. With exquisite world building and luminous detail, this is high fantasy at its best. The magic is fierce and the plot intensely twisted, but at this novel's dark heart beats a story about sisterhood, the unbreakable bonds of family, and ties that bind enough to kill."