'There's a scarlet thread of murder running through the colourless skein of life, and our duty is to unravel it, and isolate it, and expose every inch of it.'

When Dr John Watson takes rooms in Baker Street with amateur detective Sherlock Holmes, he has no idea that he is about to enter a shadowy world of criminality and violence. Accompanying Holmes to an ill-omened house in south London, Watson is startled to find a dead man whose face is contorted in a rictus of horror.

There is no mark of violence on the body yet a single word is written on the wall in blood. Dr Watson is as baffled as the police, but Holmes's brilliant analytical skills soon uncover a trail of murder, revenge and lost love.