Final Oath Of Tharvash

From publisher blurb:

In the abyssal hollows where shadow clings to stone and whispers take form, there are those who seek beyond the mortal plane, beyond the howling lords of ruin, beyond even the ancient pacts that bind flesh to the infernal. It is said that the Shade House of Tharvash has long danced upon the precipice of oblivion, worshippers of Murzakhar, the Black Spiral, the God of Rebellion, Anarchy, and the Unmaking of Chains. But one among them—driven by an insatiable hunger, by a thirst not even the great demons could slake—seeks a power yet untouched by mortal hands, a knowledge buried in the weeping fabric of the world itself.