By coincidence, I began reading Conan Doyle for the Defence in a Glasgow hairdressing salon barely two minutes’ walk from 49 West Princes Street, the address at which, on 21 December 1908, the murder at the heart this book took place. Sitting down to write my review, I gave in to a sudden urge, and in roughly six minutes was outside the door through which the murderer of “upright, formidable, churchgoing” 82-year-old Marion Gilchrist entered and left …