With hindsight we can recall the small clues that warned of what was to come. My dad would lose things, forget things. One day there was a call from the electricity company saying a bill hadn’t been paid. Mum thought this strange as dad had always been meticulous about family finances. After a hunt through some drawers, she found a discarded bundle of unpaid bills and unopened correspondence. She knew then that something was wrong.

Thankfully, the onset of dementia did not seem to trouble him. Dad seemed oblivious to its approach. Things just slipped away. Every day, for example, he used to do the newspaper crossword. Then one day he stopped. Newsletters and magazines about the Lancaster bombers in which he flew during the war would land on the doormat, but he could no longer remember anything of that vivid time of his life.

I would visit my parents’ home, a bought council house in Leven in Fife, and talk to him about what I had been up to. I had no idea how much he was or wasn’t taking in. He always smiled and nodded, but it was hard to know. It was a painful experience for all who loved him. Dementia in a family inevitably leads to gnawing regrets. You regret not talking more before the illness took hold. You regret not asking more questions about early days and youthful experiences.

I felt some of those regrets, and still do. But I was lucky. A chance find of a 60-year-old amateur film and a little detective work gave me a priceless opportunity to make a connection with my father through the fog of his dementia in his final days.

It opened up an aspect of his life that was unknown to me. Flickering onto the screen, this was a precious gift and I will be forever thankful for it. The story of how it happened is one of discovery, in every sense of the word.

MY DAD, William Rollo Mitchell, went to St Andrews University in the early 1940s. Everyone knew him as Rollo. When war cut short his studies he trained as a navigator in the RAF and flew Lancasters from airfields in Lincolnshire.

In the summer of 1943 he did 30 bombing raids; one tour of duty. Then, in 1945, after a period teaching navigation, he was called back to duty for another 22 sorties.

In later years he never talked about his experiences in the war — he was of that generation that didn’t discuss things such as that. We always said that if we could bottle my dad’s temperament we would make a fortune. You wouldn’t have to go to India or anywhere to find yourself. You would just go to Leven and buy a bottle of what made my dad so content most of the time. In his spare time, when not teaching, he loved showbusiness. Particular favourites were the Hollywood musicals, and these were the specialities of the local amateur dramatic societies in which he was a producer and performer. But all that had to be put aside once the dementia began to take hold — he simply couldn’t remember his lines.

Home for me was Edinburgh, where I was running a tourism business. In 1984 a friend and I set up walking tours of the Royal Mile giving visitors a taste of the city’s macabre history. Then we met up with restaurateur James Thomson and started the Witchery murder and mystery tours. It really caught on — 20 years later we are still doing it. Recently, as a sideline, we had begun making short films about Scotland to sell on video to tourists.

That led to a desire to get more heavily involved in film-making, so we began working up an idea for a short film called Jessica’s Will, a story about trust and relationships in a small Scottish town. To generate interest we sent out e-mail newsletters on the progress of the project, and one was sent to my mother. When she read it she thought there was something curiously familiar about it.

That’s when she went to a cupboard and pulled out a large bundle of papers and offered them to me with the seemingly innocuous comment: “Did you know that your dad made a film 60 years ago? And that he used to send out newsletters like that?” My jaw dropped. I had no idea. “Why didn’t you tell me?” I asked. She replied it hadn’t seemed a big deal — a low-budget film made by a group of friends, one of whom happened to have a cine camera, with a view to relieving the tensions of the war and putting on a film show in a local church hall.

In the bundle was a series of beautiful handwritten and hand-coloured booklets produced by something called the Monarch Films Production Society, which was just dad and his friends.

Over Christmas 2002 I devoured every detail. The newsletters were wonderful objects, full of cutout photographs, reviews, local newspaper articles, quizzes and drawings. But what fascinated me were the detailed updates on the making of an 8mm black-and-white film called And So Goodbye, most of it shot in Cardenden in Fife. My dad was to be the film’s producer and its leading actor.

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