A woman in pink lies dead in a derelict house. She is the fourth in a series of seemingly impossible suicides, which has DI Lestrade of Scotland Yard baffled. Elsewhere in London, a soldier, invalided home from Afghanistan, meets a strange but charismatic genius who is looking for a flatmate; Dr John Watson and Sherlock Holmes are meeting for the first time.

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 of a gang of international smugglers, a secret society called the Black Lotus.

A strange clue in an empty room, a blood-soaked car, a priceless Old Master, a deranged bomber. With the clock ticking, the curtain rises on a battle of wits between Sherlock, John and the shadowy stranger who seems to know all the answers.