Its low budget shows in places but this modest chiller does so many things right that it's pretty much unmissable.
Drenched in Catholic angst, it's a Hitchcockian horror-thriller with a haunting score, and a remarkably eerie performance by Paula E Sheppard, who is here playing a 12 year old when I believe she was in fact 19 at the time - lending her performance a truly other-worldly tone.
Genius casting.
Horrible setpieces and an exhausting atmosphere of hysteria makes this something of a minor classic.