The Queen’s Blade by Evelyn Ward

Go to sleep, or the Queen’s Blades will find you.
Be good, or the Queen’s Blades will get you.
Follow the edicts of the Goddess, or the Queen’s Blades will hunt you…
Will hurt you…
Will kill you…

Every citizen in the realm knows Witches are the favored Faction. That’s why a Witch occupies the throne, and why the laws of the Eternal City grant Witches far more than their fair share.
And if any of the other Factions take issue with that? They’re likely to meet a swift death at the hands of the fabled Queen’s Blades, the four assassins vowed to protect the Queen and the realm itself.

Even among the Queen’s Blades, Fey is an anomaly. As a Water Witch, her powers should have led her to a life of healing. But violence always came easier to Fey than healing ever did. The other Blades—three ruthless, savage Witches she is proud to call her sisters—love her all the more for it.

But when one of the Blades is murdered, Fey becomes entangled in a mystery that threatens the very system she vowed to protect. And every clue she finds just raises more questions.
Who can she trust? What dark secrets are being kept from her and the other Blades? And perhaps the most dangerous question of all: who really killed her sister?