Sherlock Holmes and the Deathly Fog: A Sherlock Holmes short story

Who can fight a deathly fog?Sherlock Holmes and Dr Watson are summoned into the heart of London’s slums by perhaps his strangest client yet. Children are vanishing without a trace, and the only connection is the thick fog which conceals their disappearance.Are the children alive or dead? Can the great detective discover the truth? And will the mysterious woman in black help or hinder him?