Writing Twenties Girl was like going on my own magical mystery tour. My U.S. editor Susan Kamil had once said casually, "You should write a ghost story one day." This comment stayed with me for years. I loved the idea, but didn't know who my ghost could be. I've always loved the glamour and spirit of the 1920s, and the idea came to me of a flapper ghost. A feisty, fun, glamorous girl who adored to dance and drink cocktails and get her own way. I wanted her to be a determined character who would blast into the life of someone with no warning and cause havoc. I then decided she should haunt a thoroughly modern girl, with all the culture clashes and comedy that would bring.

Having come up with this idea I loved it, so it then remained to plunge myself into 1920s research, which was no hardship at all, as I find the era fascinating. I researched vintage make-up, vintage dresses, read fiction from the period, investigated 1920s slang, and tried to channel as much I could of those feisty flappers who cut their hair short (shock!), smoked cigarettes in public (shock!), had sex (shock!) and generally rebelled in all the outrageous ways they could.

The book isn't a period piece though. It's a modern story about two girls and their sparky friendship, right here in the 21st century. One of them just happens to be a ghost from the 1920s. It's a quest, a romance, and a coming of age... and above all a comedy. It's no exaggeration to say that writing the character of Sadie made me look at life differently, and I hope some readers feel the same way. —Sophie Kinsella

When I was at college I had a bicycle which I rarely used and which sat, week after week, in the bike racks. One day I went to get it out--and found a diamante necklace twined round the spokes of the front wheel. It was an old, vintage-style necklace, one of the prettiest things I’d ever seen. On my bike! How had it got there? Had someone borrowed my bike and dropped it? Was it a romantic gift from a secret admirer? (Ok, unlikely...)

I put up a notice in college--but got no claimers. It was mine! I wore that necklace over and over--and felt as though it had somehow magical qualities. Would it have felt so magical if it were a scarf or a hat or a purse? I don’t think so.

Jewelry has a magic all its own. Precious stones have always attracted legends, myths, crimes, lust. Quite sane women will go to pieces at the sight of a big enough diamond. Even as a tiny child I was fascinated by beads, jewels, tiaras...anything that glittered. And, like books, I find it hard to give pieces of jewelry away, even after I’ve stopped wearing them.

The biggest symbol of jewelry is love. Whose heart doesn’t stop on being presented with a little velvet box? Who secretly doesn’t crave a diamond, however teeny? Of course true love is putting out the rubbish every night...but that won’t make you gasp and tilt your hand to catch the facets of light.

When I was writing Twenties Girl I knew I needed to give Sadie, my ghost character, a mission. There was something in the world she still wanted--and it didn’t take long to decide on jewelry. A ring seemed too obvious...bracelets too inconsequential...but a necklace was perfect. I wanted it to be tactile, romantic, and the kind of piece you could imagine wearing with anything. Guided by research into jewelry of the 1920s, I conjured up in my head a long necklace of glimmering yellow glass beads, with a dragonfly pendant set with rhinestones. Not priceless....but special. I could imagine Sadie twirling the beads as she danced, I could imagine her gathering them and letting them drop. I could see it as an iconic, timeless piece.

A dragonfly seemed a perfect emblem for Sadie, too--beautiful, fragile, and darting around like quicksilver. The dragonfly symbol has different meanings for different cultures--for some it’s a symbol of change, for others it represents the subconscious. In Japanese paintings, dragonflies can mean new light and joy. To some Native Americans they’re the souls of the dead. All of these interpretations are perfect for the character of Sadie--a ghost who needs to "move on" and for whom the dragonfly necklace has a meaning all its own.

The more I wrote about Sadie’s dragonfly necklace the more it came to mean to both her and me--and I hope it does to readers, too.