Sherlock Holmes must decipher a cryptic warning of impending murder that leads him into a complex web of international intrigue and secret societies. Holmes and Dr. Watson receive a coded message from a mysterious informant, which prompts an investigation into the life of John Douglas, a man whose past in a violent American mining region threatens his present safety. The narrative utilizes a bifurcated structure, shifting from the immediate investigation in a fortified English manor to an extensive flashback detailing the history of the Scowrers in Pennsylvania. Holmes operates within the logical constraints of his deductive method, navigating social hierarchies and criminal networks to expose the truth behind a staged death and a long-standing vendetta.

Discussion often centers on the unconventional structure of the novel, which spends a significant portion of its length detailing the backstory of the American criminal underworld. Readers frequently highlight the contrast between the clinical, intellectual atmosphere of the English scenes and the visceral, action-oriented nature of the flashback sequences. Critics often note that while the book deviates from the traditional short-story format of the series, it provides a deeper look into the global reach of Holmes's adversaries. The pacing is frequently described as deliberate, allowing for a thorough examination of the thematic elements surrounding vengeance and identity. Many readers appreciate the historical context provided, though some prefer the more contained mysteries found in the earlier collections.