Matthew Sweet with a review, from Lynda Neade, of the UK's first ever retrospective devoted to the portraiture of Edouard Manet. Maria Konnikova says that Sherlock Holmes can offer us the key to a world where we use our brains to their full potential. Alan Rusbridger and Matthew Taylor explore the status of the amateur in society and ask whether there has been a genuine shift in how we value the role of the non-professional. And Matthew Sweet talks to Norman Stone about his latest book: A Short History of World War II.