From the publisher's website:

To be a Summoner is to be one of a handful of beings who control the very fate of the planet Itharia. They are demigods, once mortal beings of exceptional ability now wielding vast supernatural powers that even they only partially comprehend. Nations rise and fall at their command. The world is reshaped at their behest. Legions of warriors lie at their disposal, living or dying by their Summoner's command. But so too are they tormented and imperfect beings, chosen by the Summoning Stones that give them power to continue a war that started in the heavens. Theirs is the burden of dead gods, and the curse of war unending. Together they could build a paradise, but the old ways die hard. And death has long been the currency of Itharia.