It wasn't technically an exorcism, what they did to Clare. When the reverend and his son ripped her demon from her, they called it a "deliverance." But they didn't understand that Clare and her demon--known simply as Her--were like sisters. She comforted Clare, made her feel brave, helped to ease her loneliness. They were each other's Only.
Now, Clare's only comforts are the three clues that She left behind:
Be nice to him
Remember the stories
Clare will do anything to get Her back, even if it means teaming up with the reverend's son and scouring every inch of her small, Southern town for answers. But if she sacrifices everything to bring back her demon, what will be left of Clare?