Glass Cat Eye: Short fantasy thriller novel

A preacher's daughter's excessive appetite for the dark side compromises her relationship with a young atheist; his desperation to save her catapults him into a strange world that is literally about to blow up in his face; and a theology professor turned demon hunter tries to save our world by battling a creature from the River Styx. In a hidden place where demons float in and out of earth's realm through a swirling mystical hole, what can save us?