Angel's Power — Erin M. Leaf

Ariel doesn't understand why her wings are changing colors. She doesn't know why energy flickers through her and she doesn't have time to worry about it. Demons are loose and she must help her brother lead their People.

When Suriel, the angel sorcerer, arrives and offers his help, Ariel's immediate attraction to him confuses her. She wasn't looking for a mate and is afraid to commit to anyone while her wings are damaged. And the demons are out there, waiting for the angels to show weakness…

Suriel doesn't want a mate. His power is strong, but very unstable and he is terrified that he will hurt someone if he lets anyone get too close. The only reason he came to Castle Archangel is to help defeat the demons. However, Ariel, the Alpha's sister, draws him like no other woman ever has. And when she is injured in a battle, he will do whatever it takes to take care of her.