Some people think that being a writer is glamorous. I know that I once did. I dreamed of finally getting published and all the amazing fun that would follow. I imagined traveling to distant countries, staying in city hotels and seeing the sights.

Most of these dreams came true and I do enjoy it, but sometimes it can be hard work: having to grab a coffee and manage without breakfast to be in time to travel to some school event; attending a bookshop when hardly anybody turns up; spending a night alone in a strange town on a wet Monday; visiting a big city but seeing only the inside of your hotel room. So when you actually do live the life of a writer, it's not as glamorous as some people might believe.

The same is true of filmmaking. In the spring of 2012, I visited Vancouver, Canada, to watch the movie version of The Last Apprentice: Revenge of the Witch (published in the UK as The Spook's Apprentice) being made. The film is called Seventh Son, and the name is a good choice. After all you have to be a seventh son of a seventh son just to be eligible to become a spook's apprentice.

They have created some amazing sets, designed by Dante Ferretti, winner of an Oscar for his work on Hugo. I was shown the preliminary models and artworks, then the sets themselves. They are very big and very convincing. I saw a walled city set in a huge muddy field. It was like a building site, complete with heavy machinery and workers in hard hats. There was no glamour there.

That comes afterward.

I met Jeff Bridges, who plays the Spook. He looked convincing. He believed that he was the Spook—I could see it in his eyes. Yes, he was the Spook! Then I watched him playing the same scene over and over again until he and everyone else (especially the director, Sergei Bodrov), were satisfied. There were a lot of people involved, and each one of them knew exactly what to do. It was an action scene and the Spook kept falling backward against a pillar, in danger of his life. He was covered in dust and he probably had bruises or at least aching bones the following day. It wasn't glamorous. It was hard work.

The glamour comes later.

After four months of filming, post-production began. They spent hours, days, weeks, and months editing the film until each section was perfect. Now, like a Pendle witch casting the spell called "glamour," the film comes to life and the magic will be there.

Is it a good film? The answer is yes. I watched a special preview of Seventh Son in Paris in a small private cinema belonging to Universal Studios.

Is it spectacular? The answer is yes. I watched it in 3-D, and there is a great deal of action, conflict, and combat. There are creatures of the dark that lurch out of the screen and try to remove your head, your heart, or maybe even your thumb bones. And there are witches; lots and lots of witches.