From Sherlock Holmes onwards, fictional detectives use lenses: Ocular Proof and the Spectacled Detective in British Crime Fiction argues that these visual aids are metaphors for ways of seeing, and that they help us to understand not only individual detectives’ methods but also the kinds of cultural work detective fiction may do.  It is sometimes regarded as a socially conservative form, and certainly the enduring popularity of ‘Golden Age’ writers such as Christie, Sayers, Allingham and Marsh implies a strong element of nostalgia in the appeal of the genre.  The...