The dark remains - Mark Anthony

Travis Wilder and Grace Beckett have returned to modern Earth on a mission of mercy: to get medical help for the severely wounded Beltan, a knight from the otherworld of Eldh. But as Beltan lies unconscious in the ICU of a Denver hospital, a shadowy organization plots to kidnap him for use in its cruel experiments, while sinister forces of dark magic cross the boundary from Eldh in a murderous search for Travis and Grace. Meanwhile, in Eldh itself, a young baroness, her witch companion, and their mortal and immortal friends journey to a dying city, there to confront a nameless evil that has begun to annihilate the very gods.
Somehow Travis and Grace must save Beltan and themselves, and then make their way back to Eldh, for only in this realm of gods and monsters, myth and runecraft, can they hope to defeat a demonic enemy that can shatter time, devour space, and turn existence into nothingness.