Plot Summary

Knowing the plot of The Sign of Four inside out is non-negotiable at GCSE. This lesson provides a detailed chapter-by-chapter breakdown, identifies key turning points, and maps the narrative structure so you can write confidently about any moment in the novel.

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Narrative Structure Overview

  Climax
  (Chapter 10: The Thames chase)
     /\
    /  \
   /    \       Falling Action
  /      \      (Chapter 11: Small's
 /        \      capture; treasure lost)
/  Rising   \
/  Action    \
/ (Chapters   \          Resolution
/ 3-9: The     \         (Chapter 12: Small's
/ investigation) \        confession; Watson
/                 \       proposes to Mary)
--Exposition-------\----->
(Chapters 1-2:
 Holmes's cocaine,
 Mary's visit,
 the mystery)

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Chapter 1: The Science of Deduction

The novel opens in 221B Baker Street. Holmes is injecting cocaine, and Watson expresses his disapproval. Holmes defends himself:

"My mind rebels at stagnation. Give me problems, give me work."

Holmes demonstrates his deductive method by analysing Watson's watch, deducing details about Watson's late brother — his drinking, his poverty, and his death. Watson is both impressed and hurt by the accuracy of these observations.

This chapter establishes:

• Holmes's brilliance and drug dependence
• Watson's role as narrator and moral compass
• The tension between genius and self-destruction
• Holmes's deductive method in action

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Chapter 2: The Statement of the Case

Mary Morstan visits Baker Street. She presents her case:

Fact	Detail
Her father	Captain Arthur Morstan, officer of the 34th Bombay Infantry
Father's disappearance	Vanished in December 1878 after arriving in London
The pearls	She has received one valuable pearl per year since 1882
The letter	She receives a letter asking her to meet an unknown person
The paper	Found in her father's desk — a plan of a building with "the sign of the four" and four names

Holmes, Watson, and Mary set out to meet the letter's author.

Examiner's tip: Note Watson's immediate attraction to Mary: "She was a blonde young lady, small, dainty, well gloved, and dressed in the most perfect taste." Conan Doyle uses Watson's romantic interest to create a subplot that humanises the narrative and contrasts with Holmes's cold rationality.

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Chapter 3: In Quest of a Solution

The three travel to the meeting point, where they are taken to Pondicherry Lodge, the home of Thaddeus Sholto.

Thaddeus reveals:

• His father, Major John Sholto, served with Captain Morstan in India.
• Both men were involved with the Agra treasure.
• Captain Morstan came to confront Major Sholto about his share of the treasure but died of a heart attack during their argument.
• Major Sholto concealed the death and kept the treasure.
• On his deathbed, Major Sholto tried to tell his twin sons (Thaddeus and Bartholomew) where the treasure was hidden but died before finishing — after seeing a face at the window.
• Thaddeus has been secretly sending Mary the pearls as compensation.

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Chapter 4: The Story of the Bald-Headed Man

The group travels to Bartholomew Sholto's house (also at Pondicherry Lodge). They discover:

• Bartholomew is found dead in his locked room.
• His face is fixed in a terrible grimace (a "ghastly, unnatural smile").
• A poisoned thorn (dart) is embedded in his neck.
• The treasure chest is empty — the Agra treasure has been stolen.
• On the wall, a note reads: "The sign of the four."

The locked-room mystery

This is a classic detective fiction device — the room is locked from the inside. Holmes must work out how the murderer entered and escaped.

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Chapter 5: The Tragedy of Pondicherry Lodge

Holmes investigates the crime scene. He discovers:

Clue	What it tells Holmes
A wooden-legged man's prints	One of the intruders has a wooden leg (Jonathan Small)
Small, bare footprints	The second intruder is a very small person
A creosote (tar) smell	The small figure stepped in creosote — a tracking scent
The poisoned thorn	A South American or South Asian blowpipe weapon
The locked room	Entry was through the roof/trapdoor

Holmes deduces that two people committed the crime: a man with a wooden leg and a very small accomplice.

Examiner's tip: Holmes's methodical analysis of the crime scene is a key moment for discussing the theme of science and reason. He reads the physical evidence like a scientist reading an experiment: "You know my methods. Apply them."

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Chapter 6: Sherlock Holmes Gives a Demonstration

Holmes uses the creosote trail and his dog Toby to track the murderers through London. The trail leads across the city, through streets and along the riverbank, before ending at a boat landing.

This chapter demonstrates:

• Holmes's practical ingenuity (using a dog, following scent trails)
• The geography of London — Conan Doyle takes the reader through real streets
• The contrast between Holmes's excitement and the gravity of the crime

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Chapter 7: The Episode of the Barrel

Holmes disguises himself and investigates along the Thames. He discovers that a man with a wooden leg hired a steam launch (boat) called the Aurora.

Meanwhile, the police (Inspector Athelney Jones) arrest Thaddeus Sholto — wrongly — for the murder. This highlights the police's incompetence and contrasts with Holmes's superior methods.

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Chapter 8: The Baker Street Irregulars

Holmes enlists the Baker Street Irregulars — a group of street children he uses as an informal spy network — to search for the Aurora.

Key developments:

• Holmes becomes frustrated as the search stalls.
• Watson and Mary grow closer.
• Holmes reveals his knowledge of the case to Watson, explaining the "sign of the four."

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Chapter 9: A Break in the Chain

The Aurora is located. Holmes plans the pursuit.

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Chapter 10: The End of the Islander

This chapter is the climax — the dramatic Thames boat chase.

Holmes, Watson, and Jones pursue Small and Tonga (the Andaman Islander) along the river in a police launch. During the chase:

• Tonga fires a poisoned dart at them but misses.
• Watson and Jones shoot Tonga, who falls into the Thames and drowns.
• Jonathan Small is captured.
• Small throws the Agra treasure overboard into the Thames rather than let anyone else have it.

Examiner's tip: The description of Tonga is deeply problematic by modern standards. Conan Doyle describes him using dehumanising, racist language — as a "savage" and a "little black man." A sophisticated response will analyse this critically, linking it to Victorian attitudes towards race and the "other": "Conan Doyle's portrayal of Tonga reflects the racist assumptions of the British Empire, in which colonised peoples were routinely dehumanised to justify imperial domination."

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Chapter 11: The Great Agra Treasure

The treasure chest is opened — it is empty. Small has scattered the treasure in the Thames. Mary Morstan will not inherit a fortune.

Watson, relieved that Mary is not wealthy (as this removes the barrier to a socially equal marriage), proposes to Mary. She accepts.

Holmes, meanwhile, reaches for his cocaine bottle — without the stimulation of a case, he returns to drugs.

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Chapter 12: The Strange Story of Jonathan Small

Small tells his story in a long embedded narrative (a story within a story):