Long buried secrets finally come to light as someone has been playing a very long game indeed. Sherlock and John face their greatest ever challenge. Is the game finally over?

Cast: Benedict Cumberbatch, Martin Freeman, Una Stubbs, Mark Gatiss, Louise Brealey, Amanda Abbington, Andrew Scott, Art Malik, Timothy Carlton, Wanda Ventham, Simon Kunz, Richard Crehan, Matt Young, Tam Mutu, Clare Foster