As per the author:
When psychological counselor Megan Chase promises listeners to her new radio call-in show she’ll slay their personal demons, they believe her. So do the personal demons.
Megan doesn’t know she’s the only human alive without a personal demon on her shoulder. This, coupled with her psychic abilities, makes her a valuable weapon for any demon mob-like “family” lucky enough to gain her allegiance. It also makes her a serious threat not just to the personal demons, but to a soul-sucking Legion of Hell known as The Accuser. The Accuser already has an old score to settle with Megan, and sees this as the perfect time to do it.