In the 1980's a detective (Ethan Hawke) investigates the alleged rape of a girl (Emma Watson) by her father. She says that he's the member of a Satanic cult and that they also sacrifice babies. Her father admits to the crime, though he doesn't remember it, primarily because he feels guilty about how he's treated his daughter since his wife died. A psychologist puts the girl through Regression therapy, where she comes up with this story. Is there really a Satanic cult or is she really making it all up for the attention?
This is an interesting movie, taking place during the whole "Satanic Panic" period that swept America in the last 70's/early 80's (which I always thought really stupid when I was a teenager).