Here is the synopsis, via Goodreads:
Fifteen-year-old Bridget Liu just wants to be left alone: by her overprotective mom, by the hunky son of the police officer who got her father killed, and by the eerie voices which she can suddenly and inexplicably hear. Turns out the voices are demons--the Biblical kind, not the Buffy kind--and Bridget possesses the rare ability to banish them.
San Francisco's senior exorcist and his newly assigned partner from the Vatican enlist Bridget's help with increasingly bizarre and dangerous cases of demonic possession. But when one of Bridget's oldest friends turns up dead in a ritualistic sacrifice that mirrors her father's murder, Bridget realizes she can't trust anyone. An interview with her father's murderer reveals a link between Bridget and the Emim: a race of part-demons intent on raising their forefathers to the earth in human form. Now Bridget must unlock the secret to the Emim's plan before someone else close to her winds up dead, or worse--the human vessel for a Demon King.
Trust me when I say that on August 23rd, I will be first in line for this amazing book.