I don’t have a sister but when I was younger I always wanted one. I started writing this story because I was thinking about how people’s perceptions of themselves differ from how other people see them (this is one of the reasons I love writing from more than one point of view), and how people can be jealous of others without realising that they too have enviable qualities, and it made sense for the worst possible situation to be having to live with someone you envied – your sister. It always surprises me just how evil Danielle is at times in this book, incidentally.

When I was writing this I learned a very valuable lesson: not about plotting, or writing, or character development (though I did learn more about these things too) but about something very practical: always back up your work. I had finished this and then lost the original ending in a computer crash. Painful stuff. I forget how it originally ended – it was fairly similar in terms of the outcome, but when you lose whole chunks like that you can’t ever recreate them the way that they were.