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Second Holmes novel, published 1890. Twelve chapters. Narrated by John Watson. Introduces Mary Morstan (who becomes Watson’s wife), the Agra treasure, and Jonathan Small as chief antagonist. Notable for its explicit treatment of Holmes’s cocaine use and its colonial thriller plot.
Chapter summary
| Chapter | Title | Key events |
|---|---|---|
| I | The Science of Deduction | Holmes on cocaine; Watson’s watch reading; Mary Morstan arrives |
| II | The Statement of the Case | Mary’s father vanished; mysterious pearls; the invitation |
| III | In Quest of a Solution | Meeting Thaddeus Sholto; twin brothers; Agra treasure backstory |
| IV | The Story of the Bald-Headed Man | The Sholto history; the treasure found and lost |
| V | The Tragedy of Pondicherry Lodge | Bartholomew Sholto found murdered; the Sign of Four left |
| VI | Sherlock Holmes Gives a Demonstration | Scene-of-crime analysis; thorn dart; Tonga identified |
| VII | The Episode of the Barrel | The Aurora launch; Holmes’s disguise; Baker Street Irregulars deployed |
| VIII | The Baker Street Irregulars | Wiggins; the hunt along the Thames |
| IX | A Break in the Chain | The chase; Mordecai Smith and his boat |
| X | The End of the Islander | Thames chase; Tonga shot; Jonathan Small captured |
| XI | The Great Agra Treasure | The treasure chest; it is empty |
| XII | The Strange Story of Jonathan Small | Small’s full confession; his history in India; the Agra garrison |
Key takeaways
- The Agra treasure is the MacGuffin — its ultimate loss means that Mary Morstan, rather than becoming an heiress, is free to marry Watson. Doyle uses the treasure’s disappearance to resolve the love plot.
- Jonathan Small’s confession (Chapter XII) is a substantial embedded narrative, giving the villain’s perspective and humanising him. He is a one-legged soldier whose life was shaped by the 1857 Indian Mutiny.
- Tonga, Small’s Andaman Islander companion, is a troubling figure — presented with overt racial otherness as signifier of danger — one of the Canon’s most problematic characterisations.
- Holmes’s cocaine use is explicitly addressed in Chapter I: “a seven-per-cent solution.” Watson objects on medical grounds; Holmes dismisses boredom as the greater danger. This is developed further in later stories.
- Watson’s romantic arc: his growing attachment to Mary Morstan is woven through the narrative; she becomes his wife between this novel and the later stories.
- The novel is structurally a colonial thriller — the crime’s roots lie in India, military corruption, and stolen treasure, reflecting Victorian anxieties about Empire.
First appearances
- Mary Morstan — future Mrs. Watson
- Jonathan Small — the main antagonist
- Tonga — Small’s companion
- Thaddeus Sholto and Bartholomew Sholto
- The Baker Street Irregulars (named and described in detail)