The Final Problem

A dark secret at the heart of the Holmes family finally rears its head, and it is bigger than anyone guessed. Someone has been playing a very long game, and Sherlock and Watson are left alone and defenceless against it, facing the greatest challenge of their lives. The games are manipulative and potentially fatal, and they are aimed at the people Holmes loves as much as at him. Even the victories come with a body count, and the episode never pretends otherwise.

The episode is a siege. Each test is designed to break someone, and the show keeps raising the stakes until the family secret is standing in the room with them. There are puzzles that look like riddles and riddles that look like cruelty, and the show doesn't always tell you which is which until it's too late. The secret has a name. Sian Brooke plays Eurus Holmes. And once she is in the room, the episode never lets up.

Mark Gatiss, Steven Moffat and Arthur Conan Doyle wrote it, Benjamin Caron directed. Benedict Cumberbatch and Martin Freeman carry the emotional weight, with Mark Gatiss's Mycroft, Una Stubbs's Mrs Hudson, Rupert Graves's DI Lestrade, Louise Brealey's Molly, Amanda Abbington's Mary, Andrew Scott's Moriarty, Sian Brooke's Eurus and Art Malik's Prison Governor around them.

It is not a comfortable episode, and it doesn't try to be. The series has always been about the price of genius; here it's about the price the Holmes family paid before the series began. The finale is a series of hard questions with harder answers, and it ends the way it should, with the game over and the players changed. It's a long way from the flat-share advert, and the distance is the story. Baker Street will not be quite as light again, and that's the honest ending the show owes its characters.