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.

Why is someone destroying images of Margaret Thatcher? Is there a madman on the loose? Or is there a much darker purpose at work?