Five Dark Fates by Kendare Blake

Three dark sisters rise to fight. Allegiances shift. Bonds break. Secrets surface.
Mirabella has returned to the capital, seemingly under a banner of truce.
Katharine maintains her rule over Fennbirn - for now - but at huge personal cost.
Arsinoe is lost, the responsibility of stopping the ravaging mist heavy on her shoulders.
As oldest and youngest circle each other, and Katharine begins to yearn for the closeness that Mirabella and Arsinoe share, the dead queens hiss caution. They whisper that Mirabella is not to be trusted. But even they are drawn to her power ...
The fate of the island lies in the hands of its queens.
Five Dark Fates is the epic conclusion to Kendare Blake's bestselling Three Dark Crowns series.