Dario Argento, 1977
Together with Deep Red, this is considered Dario Argento’s masterpiece.
A young American, Suzy (Jessica Harper), enrols in the Dance Academy in Freiburg. As she witnesses strange goings-on, she gets the feeling that the school is inhabited by unusual presences. It transpires that the Academy was founded by a woman whom many believe to be a witch, whose followers now try to kill Suzy. But Suzy saves herself by stabbing the founder, whose death triggers the death of all the other witches.