Damnation Marked - The Descent Series, #4

There's something in the earth deep below Elise Kavanagh's territory. A shadow is devouring demons and harvesting their souls, and it's coming for Elise next. The Union has an easy way out. They want to send Elise into hiding again with James Faulkner, a powerful witch and the man she's loved for most of her life. But she will never be able to go home again. Greater powers have other plans for Elise and her fabled power as Godslayer--plans that mean surrendering her life and blood to the most powerful demon alive.
But if she descends, there's no turning back. Once she gazes into the abyss, it will gaze back into her...and Elise will be damned forever.