Sherlock Holmes and Dr. Watson travel to the windswept coast of Poldhu Bay in Cornwall for a much‑needed rest — a rare attempt to pull Holmes away from the strain of London's relentless cases. But the peace of the Cornish spring is shattered when Mortimer Tregennis, accompanied by the local vicar Mr. Roundhay, arrives with a tale so chilling that even Holmes is stirred from convalescence.
The night before, Mortimer had visited his three siblings — Brenda, George, and Owen Tregennis — at their lonely farmhouse. They spent the evening playing whist by the fire. Mortimer left them in good spirits. But by morning, the scene had transformed into a tableau of horror:
Brenda sat dead in her chair, her face frozen in terror.
George and Owen were alive but driven into madness, their expressions contorted, their minds shattered.
Holmes and Watson investigate the farmhouse and immediately sense something unnatural — not supernatural, but deeply sinister. The fire had burned low. The air felt wrong. And the expressions on the victims' faces suggested not fear alone, but a terror induced by something unseen and inhaled.
Before Holmes can fully unravel the mystery, tragedy strikes again. Mortimer Tregennis himself is found dead in his room, seated at a table beside a smoking lamp — his face twisted in the same ghastly mask of fear that claimed his sister.
This second death brings a new figure into the case: Dr. Leon Sterndale, a famed African explorer and distant cousin of the Tregennis family. Sterndale had abruptly canceled his departure from Plymouth upon hearing of Brenda's death. His agitation, his secrecy, and his deep emotional connection to Brenda place him squarely in Holmes's sights.
Holmes discovers a strange residue near the lamp in Mortimer's room. Suspecting a combustible poison, he performs a dangerous experiment — igniting the substance in a closed space with Watson present. The result is nearly fatal:
A wave of hallucinations
A crushing sense of dread
A suffocating mental terror that overwhelms both men
Only Watson's quick action saves Holmes from the brink. The substance, Holmes concludes, is a rare African poison known as Radix pedis diaboli — the Devil's‑foot root. When burned, it releases fumes capable of inducing madness or death.
Holmes's deductions reveal a grim sequence of events:
Had learned of the Devil's‑foot poison from Sterndale
Stole some of the powder from Sterndale's African curios
Used it to murder his siblings by throwing it onto the fire before leaving the farmhouse
Intended to inherit family property and wealth (Holmes infers greed as motive)
Discovered Mortimer's guilt
Confronted him
Forced him at gunpoint to inhale the same poison in an act of vengeance
Confessed that he had long been in love with Brenda Tregennis, though bound by a marriage he could not dissolve
Holmes, moved by Sterndale's anguish and convinced of the justice behind his act, chooses not to turn him over to the authorities — one of the rare moments in the canon where Holmes allows moral justice to outweigh legal justice.
Isolation & Superstition: Cornwall's rugged landscape and local folklore heighten the sense of dread.
Science vs. the Supernatural: Holmes dismantles the villagers' whispers of curses with rational deduction.
Moral Ambiguity: Sterndale's revenge forces Holmes to confront the limits of the law.
Psychological Terror: The Devil's‑foot poison creates one of the most harrowing scenes in the Holmes canon.
First published in The Strand Magazine, December 1910.
Later collected in His Last Bow (1917).
Illustrated in its original publication by Gilbert Holiday.
This story is widely regarded as one of Doyle's most atmospheric late‑period mysteries — a tale that blends exotic intrigue, psychological horror, and Holmes's relentless logic.
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