In London in 1878, Dr Watson gets acquainted with Sherlock Holmes when they decide to live together.
One day Sherlock Holmes receives Tobias Gergson's letter, one of the bloodhoun of Scotland Yardn, who asks his help in a case of murder. A corpes is discovered with several clues and Sherlock Holmes will later manage to proove that they are wrong tracks.
After long investigations, Holmes has still found nothing. It is thanks to the experience of the inspectors Gregson and Lestrade that the finds an explanation which, grudually, clears up its firts deductions on the identity of the murederer, made when the first saw the corpse.
Holmes and Watson succeed in identifying the victim, thanks to a woman who accommodated her.
At the end of its inquiry, Holmes learns, in a newpaper, that its role in the resolution of the enigma was underestimated with policemen, were publicly thanked. The culprit is a London coachman, who, having to marry a girl who liked him, discovers that it is the victim who married him, with caused her death.