It’s a field trip with a difference in this week’s Sherlock, as Mark Gatiss takes on perhaps the best known Holmes story of them all: The Hound of the Baskervilles. Our heroes decamp to the bleakness of Dartmoor to deal with an apparently supernatural hound. Is it somehow linked to a nearby top-secret research facility named Baskerville? And can Holmes continue to function at his deductive best if he can’t fully rely on the evidence of his own senses?

Spoilers below …