Stories / The Four Novels · 1890
The Sign of the Four
Mary Morstan's yearly pearls lead to a stolen Agra treasure, a one-legged man, and Toby the bloodhound racing across London by scent.
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⚠️ Spoilers below. The analysis discusses the solution, including who did it and how it's found out.
Summary & analysis
The novel opens with the cocaine bottle and a debate about the science of detection — Holmes bored to self-destruction until Mary Morstan arrives with a tidy little problem: a vanished father, six years of anonymous pearls, and a summons from a stranger.
Bartholomew Sholto is found dead in a locked garret beside a plundered treasure room, killed by a poisoned thorn. Holmes reads the rope, the tiny naked footprints, and the creosote a wooden-legged intruder stepped in — then borrows Toby the bloodhound, and the middle of the book becomes a scent-chase across dawn London, ending at the river.
A steam-launch pursuit down the Thames catches Jonathan Small and his Andaman islander; the treasure is lost to the riverbed, which frees Watson to propose to Mary. Small's long confession — the Agra fort, the pact of four, the betrayal — again supplies the backward-running story that explains the forward one.
Deeper reading
Mood over mechanism
The Sign of the Four is the canon at its most atmospheric — opium and cocaine, a foggy launch chase down the Thames, a treasure that curses every hand it touches. Doyle, writing after a famous dinner with Oscar Wilde\'s editor, lets the prose grow richer and the melancholy deeper; the book opens on Holmes injecting himself out of boredom and closes on Watson choosing love over the case. It is a detective story that keeps threatening to become a romance and an adventure, and is the better for the tension.
Watson gets a life
This is the novel that gives Watson a heart. His courtship of Mary Morstan runs parallel to the investigation, and the loss of the Agra treasure to the river is engineered as a blessing — it removes the fortune that stood between a doctor of modest means and the woman he loves. Jonathan Small\'s confession, like the Utah flashback before it, supplies a backward-running tragedy of imperial greed. The result is the most emotionally rounded of the four novels.
Chapter by chapter
A structural map of the novel — the shape of the case, not its text. Read the full work free at Project Gutenberg.
- Ch. 1: The Science of Deduction Bored to the point of the cocaine bottle, Holmes demonstrates his method on Watson's pocket-watch, reading the life of its late owner from its case. 🎩 The surprise: from scratches around the winding-hole and pawnbroker's marks scratched inside, Holmes reconstructs Watson's dead brother's drink and ruin — a cold reading so accurate it briefly wounds his friend.
- Ch. 2: The Statement of the Case Mary Morstan lays out her puzzle: a father vanished years ago, and since then a single fine pearl arriving by post every year from an unknown hand. 🔍 Method: Holmes fastens on the dates and the regularity, treating the annual pearls not as a kindness but as a pattern with a hidden cause.
- Ch. 3: In Quest of a Solution The three set out through a fog-bound London to answer the anonymous summons that the latest pearl has carried. 💡 Lesson: Holmes withholds all judgement until the facts arrive — atmosphere and patience before theory.
- Ch. 4: The Story of the Bald-Headed Man Thaddeus Sholto reveals the great Agra treasure and his late father's guilty secret about the death of Mary's father. 🔍 Method: the backward-running history surfaces — as in every long case, the crime has a past reaching years and oceans away.
- Ch. 5: The Tragedy of Pondicherry Lodge Thaddeus's brother Bartholomew is found dead in a sealed upper room, killed by a poisoned thorn, and the treasure gone. 🎩 The surprise: a locked room and a tiny puncture — Holmes spots small bare footprints and a hole in the roof no grown man could pass, and knows at once there were two intruders.
- Ch. 6: Sherlock Holmes Gives a Demonstration Holmes reconstructs the pair from the evidence: one man with a wooden leg, and a small, barefoot accomplice who trod in spilled creosote. 🔍 Method: thorn, prints, and creosote let him describe both criminals and their route in before naming a single suspect.
- Ch. 7: The Episode of the Barrel Toby the bloodhound follows the creosote scent for miles across London — until the trail ends, absurdly, at a great barrel of the stuff. 💡 Lesson: even an infallible nose must be checked against sense; Holmes laughs at the blunder, casts back, and recovers the true line.
- Ch. 8: The Baker Street Irregulars Holmes turns his street-urchin network loose to comb the riverside for the steam launch Aurora. 💡 Lesson: Holmes trusts talent over class — a dozen invisible slum children out-search the whole official force.
- Ch. 9–10: A Break in the Chain / The End of the Islander The hunt for the launch stalls and then breaks into a moonlit chase down the Thames, ending the Aurora and its islander with his poisoned dart. 🎩 The surprise: pure deduction gives way to a breathless action climax — the canon showing it can do adventure as well as reasoning.
- Ch. 11–12: The Great Agra Treasure / Jonathan Small The iron box proves empty, and Jonathan Small confesses the whole story of the four's pact and the Agra betrayal. 💡 Lesson: the treasure, scattered into the river mud, is the canon's happiest loss — it removes the fortune standing between Watson and Mary.
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Techniques on display
Tracking & pursuit
Following a trail to its end without losing the scent.
In this story: Toby follows a creosote-dipped foot across half of London — and when the trail ends at a creosote barrel, Holmes laughs, casts back, and picks up the true line: even the best trail must be checked against sense.
Deduction & inference
Chaining evidence into conclusions on a living board.
In this story: From the pocket-watch of Watson's late brother, Holmes reads a whole biography — inherited property, drink, poverty, pawn-shop numbers scratched inside the case — the parlour-trick chapter that defines the method.
Chronology
Laying events end to end until contradictions die.
In this story: The yearly pearls, the date of Major Sholto's death, and the letter's timing only align on one theory: someone has been paying conscience-money since the day a secret was buried.
Practise what this story preaches: every technique above links to a tool or game built on the same method. The best way to learn the canon is to reason along with it.