A big thing for us early on, because, really, Holmes invented forensic science. So, in a world where everybody does it, does he still have a role? And he does, and the reason is, he is the genius in the room.

Scotland Yard absolutely take the footprint casts and the fingerprints and all that sort of stuff, but he is the only person who can fit it together, and make those massive leaps…. he says something that is outrageous, and then he shows you his working out.

SM: And even if you look at the originals, it doesn’t tend to be “I’ve measured carefully each footprint.” It tends to be something much more homely, like, “I noticed that your suit is creased.”

So, all the police have got better at is amassing the information. Interpreting that information is still an act of genius, as it ever has been. It’s actually much more compelling, because if you do the CSI stuff, you don’t feel as though you can go and do that yourself. If you’re 11, watching the show, you don’t actually have a chemistry set that good.

Mark Gatiss (MG) and Stephen Moffat (SM) on how to make Sherlock Holmes (and, for that matter, any other detective story) work in a modern, post-CSI world.