I am not a fan of bloodsports. But, growing up in posh, rural Northumberland in the 80s, it was expected that I would be. When my father, who grew up on Tyneside, moved to the country in the 70s, he rapidly began accepting invitations to pheasant shoots, as well as to grouse moors and fishing expeditions. He enjoyed the company, the sport and the hours spent out in the wild.

From about the age of eight, I was invited to accompany him on these weekend excursions, much like a child being taken to their first football matches. I disliked the early starts and standing around in freezing conditions, waiting for birds to be driven into the sky, to their deaths, over a line of booming guns. But I wanted to please my dad. As soon as I was old enough to make my own weekend plans, though, I made them. They tended to focus more on clothes shopping and cinema trips to the Metrocentre in Gateshead.

So why, years later – aged 27 and working for a film company in London – I accepted an invitation to go deer stalkingin Scotland with my father, I have no idea. Except I do. It was offered as a family holiday in the beautiful western Highlands. We had often visited the area as children and I was nostalgic for the stunning views and dramatic hills. And I still wanted to please my dad. I even took lessons, at his request, in using a .22 rifle – which, in a twist of poetic justice, recoiled and gave me a black eye the first time I tried to fire it at a paper target.

The hunting party assembled one Friday in September at the turn of the century. We started at dawn the next day in an Argocat, an open-top eight-wheel military-style vehicle that can climb near-vertical slopes at great speed. The driver was also our ghillie, a tough, wiry figure whose job it was to identify elderly or infirm deer that were selected for culling and guide us to them through wind, fog and rain.

The ghillie was tougher than the hills themselves. He hurried us up and down the bare peaks so fast and so frequently that I half thought we were training for a fell run. With every hour that passed, it felt more and more like a Buchanesque special ops mission. We were instructed to slither over a rocky streambed on our bellies, rifles clanking on our backs. We waded through bogs and hauled ourselves over marshy summits. As our quarry moved, so we changed direction continuously.

“Why are you doing this?” I kept asking myself. “What would have been wrong with a walk? Or a guided wildlife tour?”

And then, suddenly, the ghillie almost pushed me to the ground. He pointed at a cloud of fog about a hundred yards ahead. I was baffled, until the cloud lifted like a curtain to reveal – directly in front of us – one of the most magnificent living creatures I have ever seen.

I can still see the stag so clearly in my mind’s eye. Those staring dark eyes and almost puppyish large, black nose, a skeletal spread of antlers and a shaggy coat of fur, marbled with grey. He was old, but still majestic – and fit enough to have led us a merry dance over the hills. “Now!” the ghillie hissed in my ear. “Now’s your chance. Remember. You want to kill it, not wound it.”

I adjusted my position, focused down the scope once more and placed my finger on the trigger.

And, of course, I couldn’t take the shot. What on earth was I even thinking? I didn’t feel as if I was looking at an elderly beast that needed to be culled. Spectral, silhouetted against distant cloud-topped peaks, he looked more like the faded ruler of an ancient kingdom. I looked into those eyes and laid down the rifle, to the groans of the ghillie and my companions. Another curtain of mist descended; when it lifted, seconds later, the stag had vanished.

I picked up my rifle and brushed off the grass and mud. The rest of our party continued on, while I trudged back to our holiday rental. But I wasn’t dejected. I was elated. I had come – via a telescopic sight – face to face with one of the most beautiful, iconic and noble beasts of Britain, roaming free in a bleak and deserted land of his own.

It was a moment of truth and lasting inspiration. I could never have killed that stag – not in any context, for any reason. But I would, a decade later, write a story about him. Not just one book, but four, about a little boy and the stag that persuades him to help save the world’s last remaining animals. The encounter with that magnificent stag changed my life. And guess what – those stories did please my dad.

Piers Torday’s latest book, The Wild Before (Quercus Children’s, GBP12.99), is out now. To support the Guardian and the Observer, order your copy at guardianbookshop.com. Delivery charges may apply.