My friend Sarah looked me in the eye with an intensity I have rarely seen in the many years I have known her. Then she confessed: 'I have a secret. I am in love with a 17-year-old vampire called Edward Cullen. I think about him . . . dream about him. I have his photo on my desk, and his picture is my computer screensaver.' Worryingly, not only did I immediately know who she was talking about, but I heard myself declaring (several octaves higher than my normal speaking voice): 'I know! How amazing was it when he growled at...