In Canada, where Sherlock Holmes and Dr. Watson have gone to a conference on the occult, the trip home is interrupted by a chilling assignment. Lord Penrose receives the shocking news that his wife, Lady Penrose, has been murdered in the small village of La Morte Rouge. Before they can depart, a telegram from Lady Penrose—sent before her death—arrives, pleading for help as she fears for her life. Holmes, sensing something deeper at work, decides to investigate and uncover the truth behind the devastating crime.
Upon arriving in the village, the pair are confronted with a town gripped by fear and superstition. The locals are convinced that the murder is the work of the fabled monster that haunts the surrounding marshes, a creature of legend that seems to lurk just beyond sight. The tension escalates as the “monster” is reportedly seen, and even Dr. Watson witnesses a chilling description:
> the mostly ghastly apparition... like a roaring furnace spitting fire in all directions
Holmes, ever the skeptic, focuses on the human threads behind the tragedy. He identifies Lady Penrose as Lillian Gentry, a former actress entangled in a notorious murder case years earlier, when another actor was killed in a jealous rage over her. The killer, Alistair Ramson, was believed dead after a prison escape two years prior. Yet Holmes now suspects Ramson—a master of disguise—has recreated himself in the village, perhaps adopting multiple identities to stay ahead of the law.
With this new lead, Holmes turns to Judge Brisson, a figure tied to Ramson’s past through the sentence he handed down in that earlier case. Brisson’s murder, despite Holmes’ warnings, confirms that Ramson will stop at nothing to silence anyone who could reveal his whereabouts. Holmes tracks Ramson to his hidden base and discovers that a third person Ramson plans to kill is already marked. While Holmes is held at gunpoint by Ramson, Watson bursts in, but Ramson manages to slip away, leaving Holmes with more questions about the intended target.
From Holmes’ investigation, the third intended victim becomes clear: Journet, the local inn-keeper and former prison guard. Yet Journet has gone into hiding. The danger intensifies when Ramson murders Marie, Journet’s daughter, for failing to disclose her father’s whereabouts. Determined to end the threat, Holmes finds Journet and persuades him to set a trap for the killer, drawing Ramson into a calculated confrontation.
As Holmes and Watson plan to return to Britain, Journet emerges from hiding and reveals his intention to attend a church across the marsh to offer a prayer for Marie. Ramson strikes again, ambushing Journet on the marsh, only to discover Holmes in disguise. A brutal confrontation ensues, but Ramson escapes once more, only to be brought down by Journet with the very weapon Ramson had used to claim his victims—a five-pronged garden weeder.
The tale blends suspense, deduction, and a touch of the supernatural, anchoring a puzzle that tests Holmes’s analytical prowess against a cunning foe who thrives on disguise and deception. Through a series of tense revelations and carefully laid traps, the narrative culminates in a dramatic showdown that reconciles motive, opportunity, and justice, all set against the eerie, fog-drenched marshes of La Morte Rouge.
