After receiving a doctor’s diploma, Dr. Watson leaves to fight in Afghanistan. After the injury, he returns to London. Being cramped in funds, Watson is looking for an inexpensive apartment. A familiar paramedic acquaints him with a worker in the chemical laboratory at Sherlock Holmes Hospital, who rented an inexpensive apartment and is looking for a partner, since he can not afford to pay one. Holmes is characterized as a decent man, but somewhat eccentric. He is a first-class chemist, but he also enthusiastically studies other sciences.
The doctor finds Sherlock Holmes behind the study of blood stains. Thanks to its discovery, it is possible to determine the type of spot, and this is important for forensic medicine.
For several weeks, Holmes leads a measured lifestyle.
Once at breakfast, Watson reads an article that says that one can define the profession of a person and his character in dress and hands. He tells Holmes that this is nonsense, to which he replies that he wrote the article, and, being the only kind of a detective-consultant, applies this method in practice. His theory he applies to Dr. Watson, saying that he served in Afghanistan. At the bearing, Holmes determines that Watson is a military doctor, and on the swarthy face and white wrists that he was in the tropics. Watson is unwell and wounded, therefore, he was in the war that is now going on in Afghanistan.
Holmes receives a letter from the police inspector Gregson by mail. In the abandoned house found the body of a man. With him, a business card with the inscription: “Enoch Drebber, Cleveland, USA”. There are no signs of robbery and violence, although there are bloody spots on the floor. Taking Watson, Holmes arrives at the crime scene.
First the detective examines the sidewalk, the neighboring house and the soil. Then he enters the house and examines the corpse, whose face is disfigured by a grimace of horror and hatred.
On the way home Holmes explains to Watson that he guessed the cab and the horse in the footsteps on the sidewalk. Since usually a person writes at the level of their eyes, then the inscription can determine the growth. When he saw that the plaster near the inscription was scratched, Holmes realized that the killer had long fingernails. And having found ash on the floor, he determined the brand of cigars, since he was engaged in the study of ashes.
The constable, who was on duty that night, says that when he saw light in an empty house, he went into it, discovered the corpse and left. At that time, a red-faced drunk was driving in the street near the gate. Holmes realizes that it was a murderer who decided to return to the house behind the ring. He advertises in the newspaper about the find of the ring. On Baker Street comes the ancient old woman and in a rude man’s voice declares that this ring is her daughter. Holmes gives her the ring and goes after him, but loses sight of her. To Watson, he says that this is not an old woman, but a disguised young actor.
The police put a note in the newspaper that Enoch Drebber arrived in England with his secretary, Joseph Stengerson, and the murder took place on political grounds. Contending with Lestrade, Gregson tells Holmes that he arrested a certain Arthur Charpentier for murder. Finding a cylinder near the corpse, he went to the shop where the headdress was bought, and found out the address of the buyer. Drebber rented an apartment with Arthur Charpentier’s mother, behaved incorrectly in relation to his sister, and Arthur kicked him out. Inspector Gregson met with Arthur and did not have time to ask how he asked if the police suspect him of killing Drebber. Gregson suggests that Arthur hit Drebber with a stick in the stomach, leaving no trace on his body. Drebber died immediately, and Arthur dragged him into the house, leaving an inscription and a ring to confuse the tracks.
Arriving at the scene of the crime, Holmes and Watson see that death came from a knife in the side, and on the wall was the same bloody inscription. Lestrade reports that the killer was seen, his appearance coincides with the description of Holmes. In the pocket of the murdered one they find a telegram from America with the text “JH in Europe”, but without a signature, and on the table there is a box with two pills, when Holmes is quickened to see it. He tries the pills on a deadly dog. One of them is harmless, the second – poisonous. Holmes says he knows who the murderer is. A street boy’s family finds a cab for him, and Holmes puts on handcuffs for the cabman, introducing him as a murderer.
Suffering aortic aneurysm Jefferson Hope tells his story. He loved the girl who lived among the Mormons, although neither she nor her father observed their religion. Hope dreamed of marrying her, but the Mormons Drebber and Stangerson wanted her to marry their sons. They killed her father, and the girl was forced into marriage. The unhappy one died of grief in a month, and Hope vowed revenge. For many years he tracked them and finally found them in London. After settling down to work as a cabman, he lured the drunk Drebber into an empty house and offered two pills to choose from. One was harmless, the second was poison. Frightened Drebber grabbed a poisonous pill and died. Hope left the house, but forgot the ring there. When he tracked down Stangerson, he refused to take the pills, and Hope killed him with a knife.
Did not live to see the court, Hope dies in the prison cell. In the newspapers, a note appears that police inspector Gregson and Lestrade cleverly caught the killer. But Dr. Watson keeps a diary in which he writes down all the facts, and the public learns who actually caught the criminal.