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

After a harrowing tour in Afghanistan, Dr Watson returns to London to convalesce at 221B Baker Street, home to the enigmatic Sherlock Holmes. Their lives are irrevocably thrown together by news that a man has been found dead in a grimy 'ill-omened' house, with the word 'rache' - German for revenge - written in blood on the wall. This grisly discovery is complicated further by the look of utter horror on the victim's face, and the complete absence of any wounds on the body or sign of a struggle.

First published in 1887, 'A Study in Scarlet' is the remarkable first-outing of one of literature's most famous partnerships.