Now that I've at last been published in the USA, I've had some intriguing reactions from readers but it was one recent one that provoked this blog. He wrote to say that he was halfway through and enjoying Material Evidence very much. I was flattered, wrote back and, in the course of the email, asked him 'OK, whodunnit, then?'

A couple of days later, I got another, 600 word email in reply. He was still just over halfway through the book but was confident that he knew who the…