Shay has recently reconnected with her birth father Steve and agreed to join him and her half-sister Jo on a religious retreat. It is a Father/Daughter celebration of purity led by Pastor Seth. He preaches the responsibility of girls to follow the rules set out by their earthly and heavenly fathers to be a perfect untouched gift for their husbands on their inevitable wedding day.
As someone who considers Jesus Camp a horror film, I found just this opening concept of Pure to be prime grounds for horror.