Mark Lewis, works as a focus puller in a British film studio. On his off hours, he supplies a local porno shop with cheesecake photos and also dabbles in filmmaking. A lonely, unfriendly, sexually repressed fellow, Mark is obsessed with the effects of fear and how they are registered on the face and behavior of the frightened. This obsession dates from the time when, as a child, he served as the subject of some cold-blooded experiments in the psychology of terror conducted by his own scientist father. As a grown man, Mark becomes a compulsive murderer who kills women and records their contorted features and dying gasps on film. His ongoing project is a documentary on fear. With 16mm camera in hand, he accompanies a prostitute to her room and stabs her with a blade concealed in his tripod, all the while photographing her contorted face in the throes of terror and death. Alone in his room, he surrounds himself with the sights and sounds of terror: taped screams, black-and-white “home movies” of convulsed faces. At his house, he meets Helen Stephens, a young woman who lives with her blind mother in a downstairs flat. She visits his flat, where he shows her black-and-white films that were taken of him when he was a child. She is horrified to see that his father used him as a guinea pig in various experiments, taking movies of his reactions of fear.
Filmmaker and photographer Mark Lewis (Karl Heinz Böhm) spends days searching for just the right female models for his films which are studies of fear. He was raised by a psychologist father who used Mark as a subject for his own studies of fear and the exposure has left him marked psychologically so that he now is compelled to continue his search for women he murders for the camera as he films their reactions. Mark lives in the upper floors of his family house where he also has his photo lab and rents the downstairs to Helen Stephens (Anna Massey) and her blind mother Mrs. Stephens (Maxine Audley) whom he avoids until one day on Helen's birthday when the young nubile girl introduces herself to the photographer and they feel a connection. Mark trusts Helen enough to show her the films that his psychologist father took of him as a boy and the images disturb the girl but draws her closer to Mark. Mark's jobs as studio camera man for a film studio and cheesecake photographer for a local photo shop allows him easy access to women whom he murders while photographing to show their reactions to fear. When Helen accidentally sees some of his killing films she is appalled but wants to help Mark but the release of his secret is too much to bear as the police close in.