The narrative begins in the Baker Street study, where Sherlock Holmes and Doctor Watson decode an encrypted warning from an informant named Porlock, linked to the sinister Professor Moriarty. Before the cipher can be fully understood, Inspector MacDonald arrives with news of a brutal murder at Birlstone Manor House. The victim is John Douglas, a wealthy and mysterious American who settled in the English countryside. Accompanied by local detective White Mason, Holmes and Watson examine the crime scene, which presents baffling contradictions.
The victim's head has been shattered by a sawed-off shotgun, a wedding ring is missing from his finger, and a mysterious card bearing the initials V V and the number three hundred and forty-one is left beside the body. Cecil Barker, the victim's close friend, and Mrs. Douglas insist that an outsider must have escaped through the window and waded across the moat, yet Holmes quickly deduces that the physical evidence has been staged to mislead the authorities.
Through careful reasoning and an examination of the clues, Holmes realizes that the dead man is not John Douglas at all, but an assassin named Ted Baldwin who had tracked Douglas from America. Douglas himself is discovered hiding safely in a secret chamber within the ancient house. The second part of the story transports the reader back twenty years to the Vermissa Valley in the United States, detailing the terrifying reign of the Scowrers, a criminal secret society that terrorized the coal and iron districts. Birdy Edwards, a Pinkerton detective operating under the alias of Jack McMurdo, infiltrates the gang to dismantle its operations from within. McMurdo gains the trust of the local boss, John McGinty, and participates in the grim life of the lodge until he finally springs his trap, capturing the leaders and bringing their murderous rule to an end. The narrative returns to the present to reveal the lingering shadow of the past, as Douglas, having escaped his American enemies, ultimately meets his fate at sea through the orchestrated vengeance of Professor Moriarty.
