How Psycho changed my life: I'm a fan of Alfred Hitchcock's film ... but an even bigger fan of Robert Bloch's book

The images in Alfred Hitchcock's 1960 film are etched on author Chet Williamson's brain forever, but it was Robert Bloch's movie tie-in paperback that was the real Psycho

Horrifying: Janet Leigh in Psycho's infamous shower scene (Rex)

My parents took me to a lot of Alfred Hitchcock movies when I was a little kid in the 1950s. The first one I remember is To Catch a Thief, and I went on to see and love The Man Who Knew Too Much, North By Northwest, and Vertigo (though the dream sequence with the open grave was a tad disturbing). But none of those prepared me (or Mom and Dad) for 1960 and the knife to the jugular that was Psycho.

I sat transfixed and horrified through the shower sequence, felt my pulse hammer when Detective Arbogast reached the top of the stairs, and when I saw Mrs. Bates in the fruit cellar, the image was etched into my pre-pubescent brain forever, keeping me awake for many nights afterward.

And then I read the book.

It was a movie tie-in paperback with a screaming Janet Leigh and a rocking chair on the cover, and when I picked it up I realized that this book had come first, that this was the real Psycho, written by a guy named Robert Bloch. I bought the book and read through it in a flash, then went back and reread the good parts. Many times. It was great. I loved it. And what was even neater was that Hitchcock had really used the source material. Oh, there were a few changes - he'd made Norman Bates young and good-looking, not at all like the fortyish, plump, unattractive Norman of the book. But Hitchcock had kept the soul of the book and the character.

Iconic: Anthony Perkins as Norman Bates (Rex)

I read as much Robert Bloch as I could find - suspense novels like The Scarf and Terror, and short story collections like Nightmares, More Nightmares, and Blood Runs Cold. I kept an eye out for his film and TV work, episodes of Boris Karloff's Thriller, and films like The Cabinet of Caligari and The Night Walker. And on nearly every book by Bloch, beneath his name was "Author of Psycho." It was the book that would be identified with Bloch for the rest of his life.

And why not? His Norman Bates had become iconic. It was a name and a character that everyone recognized, and getting into a motel shower without thinking of Norman Bates became like hearing the William Tell overture without thinking of The Lone Ranger. Impossible.

Spring ahead many decades, years in which I had become a writer, primarily of suspense and horror, heavily influenced by Bloch, Richard Matheson, and Ray Bradbury and their superb ways of telling dark and eerie stories. I continued to read Bloch's work, and had actually met him several times, and found him one of the most convivial and dryly humorous men I'd ever come across. I once introduced him at a convention, and mentioned that I felt even more drawn to Bloch because he was born the same year as my father (1917) and shared a birthday with my wife (April 5th).

Source material: Alfred Hitchcock reading Robert Bloch's book (Rex)

Bloch left us, alas, in 1994, and twenty years later I learned that the agent for the Robert Bloch estate, who was familiar with my work, had recommended me for a project that the estate had conceived with Macmillan Entertainment, which was to write something that hadn't been done before - an immediate sequel to the original novel, Psycho, which would take place right after Norman Bates was committed to the State Hospital for the Criminally Insane.

Bloch had written two sequels: Psycho II, which took place twenty years after Norman was committed, and Psycho House, which occurs after Norman is long gone. There were film sequels, as well as the TV prequel, Bates Motel, but none of these were set in Bloch's Psycho universe, as Psycho: Sanitarium would be.

I tweaked the original idea, got my concept and outline approved, and went to work, crawling inside the skin of Norman Bates for nine months. It was surprisingly enjoyable, since I'd always found Norman to be quite pleasant and empathetic company. It's primarily Mother, after all, who causes the trouble.

The editors and estate were pleased with the final product, and I was delighted when Robert Bloch's daughter told me that she thought her father would have been very happy with the book. That was the highest praise I could imagine.

To be trusted with such an iconic character, and to follow in the footsteps of a writer who created not only that character, but also an entire genre of fiction, has been a dream come true. I can only hope that I served Robert Bloch, and his immortal and haunting creation, well.

If not, I can never take a shower again...

Psycho: Sanitarium is published on 12 April by Canelo, price £3.99 in eBook.