The Half-Angels
Andrew Lovesey

The book was like no other he had ever seen. The language was alien to the Earth, and the illustrations seemed to spell a deadly, dreadful story. The book was a gateway: a transtemporal link point between two worlds. And soon he found himself in that strange other world. It was a weird, alien place of soul-destroying danger, a place in which he had a quest. To survive, he must hunt down the lost daughter of the witch-king, a girl who might be an angel. Or a demon.