This is an extended version of a talk given at the Crime, Thriller and Mystery Books event, Hawkesbury Upton Literary Festival, 30 April 2022.    This is a "long read" and if you prefer to download and read it, there is a pdf version on my website here .      “How are you this morning, Betteredge?” asked Franklin Blake.   “Very poorly, sir,” answered Gabriel Betteredge.   “Sorry to hear it. What do you complain of?”   “I complain of a new disease, Mr. Franklin, of my own inventing. I don’t want to alarm you, but you’re certain to catch it before the morning is out.”   “The devil I am!”   “Do you feel an uncomfortable heat at the pit of your stomach, sir? and a nasty thumping at the top of your head? Ah! not yet? It will lay hold of you…, Mr. Franklin. I call it the detective-fever; and I first caught it in the company of Sergeant Cuff.” Wilkie Collins, The Moonstone   The new disease of Detective Fev...