I had just got married when I started writing my fourth novel. I'd come back from honeymoon, moved into our first house - a gorgeous little carriage house in London - and made my office on the third floor, overlooking the treetops in North West London. I thought, given how my art had imitated my life, I would write about an engagement, the planning of a wedding, the trials and tribulations of suddenly inheriting a new family who weren't exactly what you expected.

I started Chapter One, and sat back, halfway through, running my fingers through my hair. Bored. I was bored and the words I was writing were boring. I didn't want to write the same old first person thinly-veiled account of my life. I wanted to do something bigger. Broader. Something that had some meat on its bones. I wanted to write about friendship, I decided. About a group of friends who had known one another since University, who were now in their thirties and still trying to pursue their dreams.

Cath was my first female protaganist who wasn't based on me. I loved her. I loved her realness, and her friendship with Si. Then Lucy, and Josh - all of them felt, very quickly, like real people and like friends, a sure sign you have got your characterisation right.

Towards the end of the book, Si has a crisis, and initially he was going to be fine, but when I reached that point, his character took over, the course of the story, and I knew it couldn't end the way I thought it was going to, even though that was so much quicker and easier. I put the writing on hold, and spent weeks doing research, and to this day I'm glad I did. The trajectory of Si's life is far more honest, even though it was frightening, at the time, to deal with such a big medical issue I knew nothing about.

For me Bookends marks the start of my foray into commercial fiction, away from what has always been thought of as more traditional chick lit - single girl in the city trips around in manolos looking for Mr Right. From designer labels on every page in Mr Maybe, I consciously avoided them with this, wanting to write something less fluffy, less superficial. Of the earlier books, it remains one of my favourites.

What Do You Think?