The Lying Detective

Culverton Smith is the most chilling enemy of Sherlock Holmes's long career, and the episode sets him up carefully. Smith is powerful and respectable, the kind of man who appears on television to talk about kindness. And he has a very dark secret. Holmes takes the case knowing he is outmatched in the usual ways: Smith has money and reputation to burn, and every avenue Holmes tries seems to close behind him.

The episode is a psychological duel rather than a chase. Smith is unassailable, which forces Holmes to fight badly: the show's hero has rarely been so fragile, and that fragility is the point. He knows he can't win by being cleverer, so he has to be something else, and watching him try is uncomfortable in the right way. The episode also does something rare: it lets Watson be the strong one, holding the line while Holmes falls apart. The familiar supporting cast stays close, with John anchoring the story, Mycroft hovering, and Mrs Hudson, Molly and Mary providing the domestic weight that keeps Holmes human.

Steven Moffat, Mark Gatiss and Arthur Conan Doyle wrote it, Nick Hurran directed. Benedict Cumberbatch and Martin Freeman lead, with Toby Jones as Smith, Una Stubbs as Mrs Hudson, Rupert Graves as DI Lestrade, Mark Gatiss as Mycroft, Louise Brealey as Molly, Amanda Abbington as Mary, Lindsay Duncan as Lady Smallwood and Sian Brooke as Elizabeth.

Toby Jones is the kind of casting the show does best: a beloved actor playing a monster behind a smile. Smith is the reminder that the scariest people aren't in the shadows. They're the ones giving the interviews. The episode gets under the skin the way the best Sherlock outings do, and it proves the show didn't need a bomb to be frightening. It just needed a man with a secret and a straight face.