Believing in Blue

Wren received something for her eighteenth birthday that she was fairly sure was one of a kind: sky-blue wings. But along with those wings comes the knowledge that her father had a surprisingly practical reason for abandoning her when she was eight. In his letter to her, delivered via talking raven, she learns that it's up to her to save billions of humans and Winged Blue from a threat that's on the horizon and closing in fast. She is to travel to the world of the Winged Blue thirteen days ...