Organised criminality and violence appear frequently in the Holmes stories. A Study in Scarlet imagines Brigham Young's nascent Mormon state as a tightly knit conspiratorial organisation, exerting uncompromising control over its membership even beyond its notional borders. An ideological conspiracy of a very different kind lies behind the surreal menace of ‘The Five Orange Pips’, in which the Ku Klux Klan enforces its organisational rules through fear-inducing symbols, followed by swift and merciless punishment. The clues in this story reveal the organisation's global reach: at their home in Horsham, the Openshaws receive letters from the Klan postmarked Pondicherry, Dundee and East London; Holmes discovers that the murderers of John Openshaw are led by the captain of the barque Lone Star, registered in Savannah, Georgia. The Sicilian Mafia is behind the theft of the Borgia Pearl in ‘The Adventure of the Six Napoleons’ (1904), and ‘The Red Circle’ features another Italian crime syndicate. The protagonists of ‘The Golden Pince-Nez’ turn out to be Russian Nihilists, one hiding from his former comrades, the other on a mission to save her lover from Russian tyranny. Theft and fraud by organised gangs are the centre of ‘The Red-Headed League’, ‘The Engineer's Thumb’, ‘The Resident Patient’, ‘The Greek Interpreter’ and ‘The Dancing Men’, while the greatest crime syndicate of all is overseen by Professor James Moriarty, as we discover in ‘The Final Problem’, ‘The Empty House’ and The Valley of Fear.

The figure of Moriarty, ‘organiser of half that is evil and of nearly all that is undetected in this great city’ (Memoirs, 252), embodies a conspiratorial, totalising view of criminality that contrasts with that of most of the other sixty Holmes stories, in which criminality and human folly come in many and various forms. Moriarty's spider's web with ‘a thousand radiations’ (252) implies that crimes are not random or accidental but coordinated and concerted; their patterns are evidence of human agency and control. Moriarty's crimes are of a different order to the crimes that Holmes imagines to be taking place in the ‘scattered houses’ of ‘the smiling and beautiful countryside’ as he travels to Winchester with Watson in ‘The Copper Beeches’: