Shadow Dreaming by Yasmine Galenorn

As the demonic threat grows, Penn, my best friend, becomes the target of the local chapter of Brim Fire. We think they’re determined to open the portal she watches over, and when they kidnap her, we go on high alert, attempting to save her life.
As we come closer to the truth about her kidnapping, more of my newly developing demonic powers go into overdrive, and—panicked over Penn’s abduction—I give them free rein.
Now, as we rush to save her, I must struggle with my desire to go all-out demon on anybody who gets in my way.