The 'What Happens Next?' Factor - a recipe for success?

It's what every writer seeks, isn't it? That magic ingredient which will make a book into something people don't just want to read, they have to. They can't put it down, they wish it would go on for ever.

I keep asking myself what the secret is. All the time I'm writing, I'm partly aiming at the end product (and having fun) and partly hoping that by doing it I will learn how to do it.

And I read, and read, and read, books other people have made popular. Harry Potter. So many critical readers have picked holes in JK Rowlings's writing, but I devoured every word. The Girl with the Dragon Tattoo. Larsson is full of weaknesses my writers' workshop wouldn't have let out the door - if he were capable of submitting an extract sufficiently succinct to qualify for critiquing - but I couldn't put the books down until I'd finished the trilogy.

Good writing alone is not enough: what you need is character. That was the first thing I learned. The protagonist has to be quirky enough to intrigue, vulnerable enough to attract sympathy and sufficiently risk-prone for us to fear for their safety - all of which apply to Lisbeth Salander. But that wasn't what kept the pages turning. As I've said before, I believe story is what really matters. For what it's worth, my vote for character, plot and skilful writing in a blockbuster goes to Suzanne Collins and The Hunger Games.

All very nice and analytical, but it still hasn't given me my answer.

Oddly enough, the most useful insight came from my own writing - not, I hasten to add, that I'm holding myself up as an example of someone who's achieved success: just that I've found a way of articulating what I'm trying to do which I find helpful, and maybe you will too.

I've been stuck for a long time trying to decide which of a small number ideas will be the starting point for my next book, and for all my doubts about it, I keep coming back to one of them. It could be because the lead character is beginning to get a hold on me (check), but the real revelation came to me when I realised I couldn't let that embryonic story go because ...

I wanted to know what happened next.

That's it. So simple, and so crucial. What drove me through seven volumes of Harry and 2,000+ pages of Larsson. What's sucking me into my own work in progress. I'm trying to express a formula for what makes a book un-put-downable. And that's it. The ability to keep the WHN (What Happens Next) question always in the reader's mind

Next time I edit an MS, I shall be checking for typos, plot holes and the WHN Factor.