For all of his phenomenal achievements, Alfred Hitchcock is probably best known for Psycho, and in particular the scene in which – spoiler alert – a man dressed in his dead mother’s clothes stabs a naked woman in a motel shower. Audiences in 1960 were traumatised. In a recent documentary about that one scene, 78/52, Peter Bogdanovich remembers the “sustained shriek” that filled the cinema when Psycho premiered in New York. But Hitchcock had an even more shocking film planned just a few years later. It would have been called Kaleidoscope. Determined to catch up with Europe’s most innovative directors, Hitchcock wanted to apply their radical methods to one of his own typically dark narratives. If he had succeeded, we might currently be celebrating the 50th anniversary of a boundary-pushing, taboo-shattering masterpiece. But it wasn’t to be. Kaleidoscope was deemed so transgressive that not even the man behind Psycho was allowed to make it.

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Hitchcock had hoped that the film would go into production in 1967. He had just been given an honorary Oscar, the Irving G Thalberg award, and Francois Truffaut’s book of interviews with him had just been published, so his place in the pantheon of all-time great directors was secure. On the other hand, his last two releases, Marnie and Torn Curtain, had both been disappointments. Torn Curtain, Hitchcock’s 50th film, had gone down especially badly when it came out in 1966. “There is a distracted air about the film,” wrote Richard Schickel in Life magazine, “as if the master were not really paying attention to what he was doing.” Schickel went on to complain that the “mechanical” Torn Curtain was the work of a “tired” Hitchcock repeating “past triumphs”. Something had to be done.