Diabolique

“The movie has fun with the usual whodunit details: The split-second timetables, and the sleepy old guard who must open the gates to let anyone in or out of the school grounds...Then comes the ending, inspired by "Gaslight," in which a woman is either going mad, or nothing is as it seems. "Diabolique" is so well constructed that even today it works on its intended level — up until, say, the last 30 seconds.”