Wrathful Mortals by Caroline Peckham

The gods play havoc with our souls.
Callie:
I’m torn in two.
The mark of the gods has bound me to my mortal enemy, and not even the most desperate yearnings of my heart can break this tie.
Between the slayer’s vow and the cruel tricks of Idun, my free will has been stolen from me.
All I can hope for now, is that my sister and I can find a path to salvation, but it feels as though we’re walking a path to our ruin instead.
Montana:
I made my choice, and there’s no turning back.
The world has finally offered me the liberty I craved, so why does my heart keep begging me to return to the monster I left behind?
I sense a danger brewing on the horizon, something coming this way that we can’t escape. And even as my thoughts settle on a faraway land where we can leave our hellish past behind for good, I fear it won’t be that easy.
The games of the gods have only just begun.