The first Sherlock Holmes story, it starts with an explanation of how Dr Watson came to meet Holmes . . .
In 1878 Watson takes his degree of Doctor of Medicine at the University of London, and becomes a surgeon in the Army. Caught up in the 'second Afghan war' he is badly wounded in the shoulder and sent home. Back in London without kith or kin, he finds life in a hotel a lonely and expensive existence. One day an old acquaintance called Stamford tells Watson of an eccentric chap looking for someone to share rooms in Baker Street. They meet Holmes at the hospital laboratory where he's just discovered an infallible test for bloodstains. Holmes' first words to Watson are: "How are you? You have been in Afghanistan, I perceive." The doctor is amazed, and a pattern is established: Holmes' skill mesmerizes Watson who in effect acts as the foil to Holmes' magician. They move into the rooms at 221b Baker Street, and over the next weeks get to know one another. Watson is still weak from his injury so spends much time at home wondering what it is Holmes actually does for a living. With his customary lack of modesty, Holmes tells him, "I am the only one in the world. I'm a consulting detective." Holmes explains to Watson how he helps the police and individuals when they are at a loss, and how he bases all his deductions on careful observation. Holmes receives a letter from Tobias Gregson, the 'smartest of the Scotland Yarders', asking for his help in solving a mysterious murder which is baffling Gregson and his colleague and rival Lestrade. Holmes sets off at once for the crime scene inviting Watson to join him.
In an empty house on the Brixton Road a well-dressed man is found dead but there is no wound on his body. On the wall the word 'Rache' is written in blood. The dead man is apparently Enoch J. Drebber of Cleveland, Ohio. In his pocket is a letter to Joseph Stangerson, his secretary. A ring is found. Holmes puts an advert in the newspaper saying the owner of the ring should come to Baker St to collect it. An old woman turns up for it, and when she leaves, Holmes sets off in hot pursuit. He is outwitted and the old woman disappears into the night.
Gregson goes to the Charpentier boarding house where Drebber and Stangerson had been staying and believes he has discovered the murderer: the son of Madame Charpentier. He had a quarrel with the drunken Drebber when the latter was rude to his sister. Meanwhile Lestrade discovers that Stangerson has been murdered, stabbed in a hotel room near Euston station. A small box containing two pills was found near the body. Holmes cries out, "The last link! My case is complete." The two detectives urge Holmes to explain everything, but suddenly Wiggins, the 'spokesman of the street Arabs' (a group of young boys who work as Holmes' runners), arrives with a cabman. Holmes bends down over a bag and asks the cabman to help him with its buckle. As he does so, Holmes snaps some handcuffs on him, and tells the detectives it is Mr. Jefferson Hope, the man responsible for the two murders.
Once arrested, Hope is happy to tell his tale because he knows he does not have long to live; his aortic aneurism will soon burst. He explains his conduct, then is found dead in his police cell the next morning with a smile on his face. His heart lasted out just long enough for him to get his revenge on the men who ruined his life more than twenty years ago.
Hope was in love with Lucy Ferrier, the adopted daughter of John Ferrier who lived in the Mormon community (after he and Lucy were rescued by the Mormons when they were starving in the desert). But Hope was prevented from marrying Lucy because the Mormon Elders had decreed that Lucy should marry either Drebber or Stangerson, the sons of prominent Mormons. One night Hope helped the Ferriers to escape, but while he was off by himself hunting for food, the Mormons arrived, killing John and kidnapping Lucy. Hope returned to the camp to find John's newly dug grave and Lucy gone. He returned to the mountains near the Mormon community and found that Lucy had been forced to marry Drebber. She died within a year, and Hope swore revenge. His failing health and lack of funds forced him to put off his plans for some years. Then he learned that Drebber and Stangerson had fled to Europe. He followed them as best he could, finally catching up with them in London. He took a job as a cabman and followed them about. One night Drebber hailed his cab when blind drunk. Hope drove him to Brixton Rd (where by chance he had a duplicate key to an unused house) and told him he had a choice: Hope had prepared two pills, one containing poison, one without. Drebber could chose which pill he took. With Hope's knife at his throat, Drebber took a pill, and Hope the other. Bad luck, Drebber. The blood on the wall came from Hope's nose (in the excitement he had a nosebleed) and he wrote the German word for revenge on the wall as a red herring, hoping the police would suspect some foreign socialists. Hope tracked down Stangerson and made him the same offer of the pills, but he refused, so Hope stabbed him to death. To avoid attracting attention to himself, he continued working as a cabman, intending to disappear once interest in the case had died down.
How did Holmes catch him? Drebber had no wound, but his lips smelt sour (--> must have been poison what killed him). Drebber's pockets were still full of money when he was found (so he wasn't killed for financial gain). The ring pointed to a romantic feud. Holmes telegraphed the head of police in Cleveland asking for information about Drebber's marriage. The reply told Holmes that Drebber had applied for the protection of the law against an old rival in love called Jefferson Hope. By carefully observing the tracks in the mud outside the crime scene, Holmes surmised that the cabman who drove Drebber there had gone with him into the house, leaving his horse unattended. Ergo the murderer was one of London's 'jarveys'. Holmes sent his 'street Arabs' to every cab proprietor in the metropolis until they ferreted out Jefferson Hope.