I can recall being genuinely scared when I first saw this film in the early 1970s. Young women are being found murdered. What makes their crimes especially heinous is the look of sheer terror found on their faces - and that is what is further perplexing the pursing Scotland Yard detective "Gregg" (Jack Watson). Meantime, actress "Vivian" (Moira Shearer) is filming her new movie and on the set is the camera-obsessed "Mark" (Karlheinz Böhm) who rents out the bottom part of his sprawling house to a group of youngsters. Usually keeping himself to himself, he is befriended by "Helen" (Anna Massey) and soon a relationship, of sorts, develops as she takes an interest in both him and his films. When tragedy occurs at the studio, the police investigation initially includes the sound stage crew, and gradually the plot unfolds in a dark and menacing fashion. Böhm and Massey are great here and under Michael Powell and Otto Heller's creative direction and photography, deliver us an intimate and well paced story that takes it's time, but does so in a cumulatively effective fashion. The dialogue is disarmingly potent too - there is something almost childlike about "Mark" and almost maternal about "Massey", illustrative of the underlying psychology of the story. On a dark night with the rain battering against the window, this is about as good as cinema gets.