Frenzy is Hitchcock's most pessimistic film. It is a portrait of a fallen world, a modern wasteland where moral values have entirely disappeared, the landscape has been defaced and polluted, and man (always, for Hitchcock, a very imperfect thing) has been beaten down and dehumanized so thoroughly that no redeeming qualities are left. (p. 1)
Frenzy develops around a thematic structure common to many of Hitchcock's films: the hero (man or woman; in this case a man) gets caught up, usually by accident, in a series of irrational events from which he must extricate himself. What he experiences in doing so generally has a therapeutic effect on him; by the end of his adventures, the hero often has gained a new sense of human responsibility and commitment. (p. 2)
It seems that over the years Hitchcock's belief in the possibilities of man to save himself and his world have diminished. His later films have revealed a tendency that leads eventually to the total pessimism of Frenzy. The ending of The Birds, while we do see a new Melanie Daniels … is tenuous. She has changed, and there is the possibility of marriage with Mitch Brenner …, but there is a catch. We see them driving off to San Francisco, but the final shot is of the birds, a reminder of the irrational and precarious nature of our existence. Perhaps they won't make it to San Francisco; perhaps the birds are stronger than man's ability to remake his world. Topaz brings us even closer to the final theme. It is a picture of political chaos, which results in many deaths. The world is saved from nuclear destruction, but the final scene of a man tossing into the garbage can a newspaper announcing that the Cuban missile crisis has been averted demonstrates Hitchcock's concern over man's growing indifference to life. In Frenzy Hitchcock pulls no stops in giving us a portrait of total decay. Civilization seems to have died, and, with it, man's spirit. (p. 10)
Gabriel Miller, "Hitchcock's Wasteland Vision: An Examination of 'Frenzy'," in Film Heritage (copyright 1976 by F. A. Macklin), Vol. 11, No. 3, Spring, 1976, pp. 1-10.