It’s funny how even the smallest things can change your life. I was the headteacher of a village primary school, married, late thirties, with two kids and a rabbit. I wasn’t expecting any surprises. Then, one hot August afternoon, I went for a walk and a horsefly bit me. It hurt and I flicked it off, but as I watched it circle me for another attack, I thought: what if there was a little pilot in there, flying it like a fighter plane?

And that was the turning point. I decided to try to write a book based on my surreal daydream.

With the rest of the house still sleeping, I would get up at 3am and write for hours, constructing a story about a nightmare world in which young pilots trained to fly specially converted wasps into battle against horseflies and mosquitoes. I would write at weekends, holidays, whenever I had a free moment.

When at last The Dreamwalker’s Child was finished, I bought a copy of the Writer’s Handbook and saw that the literary agents Conville Walsh were “particularly interested in first novelists”. Ooh, I thought, that’s me. So I sent off my manuscript and was told it would take about three months for them to get around to reading it. Three months and one second later I emailed a polite enquiry and steeled myself for the inevitable disappointment. But, to my amazement, they said they wanted to meet me. I felt like I’d won the lottery.

I arrived at their offices in a tremendous downpour, dripping all over their floor and listening to a 23-year-old fresh out of Cambridge say, “To be honest, I’m not a great fan of fantasy and I’m not sure about the insects. But still, I think you may have something here...”

The 23-year-old turned out to be a literary agent called Ed Jaspers, and he quickly became my friend and mentor. “Okay, Voakey,” he said after I’d done a few rewrites, “I think we’re ready to go with it now.”

That weekend, I couldn’t sleep. I phoned Ed. “What if no one takes it?” I asked. He laughed. “Shut up, you tart.”

The following week, I was about to take assembly when the phone rang and it was Ed, telling me that four major publishers wanted to buy my novel and there was going to be an auction. I asked another member of staff if they would mind taking assembly while I sat down and had a cup of tea.

A couple of days later I went to meet the publishers. Back when I was a teenager reading TS Eliot’s Four Quartets, I had dreamed that one day Faber Faber might publish something I had written. Now I found myself drinking their coffee, eating their biscuits and listening to a lovely editor say nice things about my book. Afterwards, clutching my helium balloon with the words “Fly with Faber” written on it, I said, “Shall we choose them?”

“Hang on,” Ed replied, taking my balloon away. “Let’s meet the others first.”

One of the other publishers gave me a smart tie covered in dragonflies.

Another presented me with a magnifier containing little plastic insects.

The last one we visited had decorated the office with insects. It was wonderfully surreal and at that moment I realised that, whatever happened in the future, there would never be another day quite like this one.

I signed a two-book deal with Faber and, after all the excitement and champagne had worn off, I realised that it would be another year before the book was actually published. Meanwhile I still had a school to run. I also had to write the sequel. So I was pretty busy for a while. When I’d finished the second book, I thought, “I don’t know if I can do that again”.

With an Ofsted fast approaching, I put thoughts of book three to one side and decided it was time to give my life some serious thought.

Then, Faber unexpectedly offered me a new three-book deal. The Dreamwalker’s Child was bought at auction by Bloomsbury US and it dawned on me that I wouldn’t have to do two jobs any more.

The last days of the summer term passed in a blur and suddenly I was standing in front of the school that I loved, taking my final assembly. At the end, a little girl came up to me and took hold of my hand. “Please don’t go,” she said.

In September last year, I was invited to Faber’s annual conference. When I’d finished speaking, I wandered out into the sunshine and found DBC Pierre sitting on a bench. We got chatting and I told him it was my first day. “That,” he said, “has got to be celebrated.” And so it was that, on a day when I would normally have been worrying about setting targets, unblocking school toilets and singing “Autumn Days”, I found myself sitting outside a sunny London pub, watching the day go wobbly at the edges and feeling as though a new life was about to begin.

So, take it from me. The next time you see a horsefly buzzing around your head, keep your wits about you. It might just be the start of something.

Steve Voake was headteacher of Kilmersdon primary school, Somerset. His latest book is The Web of Fire, published by Faber