It is one of Roman Polanski's most brilliant films: a deeply disturbing, horribly convincing psychological thriller that is also that rarest of things: a scary movie in which a woman is permitted to do the killing. Catherine Deneuve's glassy stare of anxiety dominates the movie: it is like Janet Leigh's empty gaze at the end of the Psycho shower scene. Polanski clearly took something from that movie, as well as from the chaos, squalor and mania in Joseph Losey's The Servant (1963).

Carol (Deneuve) is a shy, beautiful young French woman living in London with her worldly sister Helen (Yvonne Furneaux) in a shabby mansion flat in South Kensington. (They could in fact be Belgian; Carol talks about a family photo being taken in Brussels.) She is intimately disgusted by her sister's obnoxious (and married) boyfriend, played by Ian Hendry, a stalwart character actor of the times, and by the way this man comes over for noisy sex in the bedroom next to hers, and casually leaves his razor in her tooth-glass.

Carol is horrified by other men's desire for her, even when her admirer, Colin (John Fraser) is a transparently decent man whose honest love might be exactly what she needs. But her fear of sex develops into a neurotic fascination and horror of dust and dirt of all kinds, a condition that escalates into agoraphobia and paranoid episodes. The nightmare she creates for herself is one of the most disturbing things I have ever seen in the cinema: the way scenes will end with bizarre hallucinations and jolts; the "assault" scene played out to the amplified ticking clock; the sudden, giant cracks she imagines on switching on a light – they always creep me out with a thoroughness that run-of-the-mill horror movies never achieve. There can't be many other films which so plausibly show an entire, warped world created from a single point of view.