A mysterious cipher is being scrawled on the walls around London. The first person to see the cipher is dead within hours of reading it. Sherlock plunges into a world of codes and symbols, consulting with London's best graffiti artists. He soon learns that the city is in the grip a gang of international smugglers, a secret society called the Black Lotus.

• Steven Moffat
• Arthur Conan Doyle
• Mark Gatiss

• Toby Jones
• Amanda Abbington
• Amanda Root