In the stews of London's East End, an outbreak of insanity sees ordinary men and women reduced to gibbering, incoherent wrecks; a mysterious creeping fog hides terrifying apparitions within that rob the wits of all who see them and even inspire suicide. Sherlock Holmes, in the infancy of his detecting career, deduces a connection between these sinister "shadows" and an Oriental drug lord who is bent on expanding his criminal empire. Yet there are even more sinister forces at work, as the great detective faces a challenge so fearsome and deadly that his career may be over almost as soon as it has begun.