Thank you to all the people who helped me to write this book: to Dr Debra Bradley, Peter Parish MD, Lavinia Payne, and Dr Mark Perry, for answering my particular scientific and medical queries; to the novel-writing group, Christina, Maggie, Marion, and Natasha, for support, criticism and hugely enjoyable discussions; to all the readers who asked how I was getting on; and to Mike for solving the various mysteries that my computer dreams up.