* DesignatedVillain: The murderous duo that the protagonists chase. The reader sympathizes with their attempts to free humanity by killing the Old Ones. Unusually for this trope, the YMMV aspect is that some readers would debate if the murderous duo ''were'' designated as the villains of the piece, or if [[HeroAntagonist they were intended to be the heroes]].
* GeniusBonus:
** During [[ShowWithinAShow the historical play]], [[NamesToRunAwayFromReallyFast "The Czar Unanswerable"]] is mentioned as one of the {{Eldritch Abomination}}s that took over the world seven hundred years earlier. At the end, [[spoiler:the narrator refers to "recent events in Russia" as being a Very Bad Thing, and gives the year as 1881. What happened in our universe's Russia in 1881? [[CartoonBomb The assassination]] of the reformist Czar Alexander II, which led to a brutal crackdown on any hint of liberalism [[YouKilledMyFather by his successors]] (and, in turn, to further extremism from the anti-monarchists which led to the 1917 Russian Revolution, the Bolshevik takeover, and all its subsequent wonderfulness). If someone actually [[DidYouJustPunchOutCthulhu managed to kill one of the Old Ones]], the retribution from his family would be ''quite'' unpleasant.]]
** Since Holmes is implied to be trying to develop nuclear weapons (and if anyone can pull off a one-man Manhattan Project it's Holmes) he'll likely be integral to the success of the ultimate revolution. The real question, though, is whether they can manage to avoid the collapse of the 'Soviet Union' or make a sensible Detente with the Eldritch Horrors.
*** Another possible reading is that Holmes already succeeded in developing a functioning thermonuclear device, and that this is how he was able to actually kill the Czar Unanswerable.
** Sherry Vernet's name reflects the canon, as [[spoiler: Holmes makes an offhand comment that his grandmother was the sister of an artist named Vernet.]]
*** "Sherringford" was also an early first name Doyle considered for Holmes.
** Readers who are particularly knowledgable about Sherlock Holmes will [[spoiler: realize earlier the protagonists' real identities as Moran and Moriarty]].
*** It's pretty common for professionally published pastiches to [[WritingAroundTrademarks write around trademarks]] by leaving characters unnamed, so the narrator only referring to the detective as "my friend" is unsurprising. [[spoiler: This puts the audience off from the REAL reason that they remain unnamed until the end. After all, the vast majority of the Sherlock Holmes story are in the public domain.]]
** The advert at the start of chapter 4 claims that V. Tepes can help you if you are feeling quinsy. "Quinsy" is an archaic term for a peritonsillar abscess, but it may also a be DoubleEntendre referencing Quincy Morris, a character from ''Literature/{{Dracula}}'' who often gets AdaptedOut.
** The ShowWithinAShow plays include several historical and Lovecraftian references, but noticeably do NOT reference the most famous eldritch play, ''Literature/TheKingInYellow''. [[spoiler: As the play in question drives the audience mad, its exclusion is a hint as to the HeroAntagonist nature of the killers.]]
* MagnificentBastard:
** "Rache", the murderer of [[AssholeVictim Prince Franz Drago]], is a revolutionary seeking to tear down the [[EldritchAbomination Great Old Ones]]. Rache [[LuredIntoATrap lures the Prince into a trap]] by promising him a girl to feed upon, whereupon Drago is led to Rache's partner to be murdered. When the detective of the story tracks Rache down under the alias Sherry Vernet, Rache easily deduces his true identity and eludes capture, throwing the country into uproar while he simply hides in the rookery of St. Giles where the police don't dare tread. While ruthless, Rache is dedicated to the defeat of the Old Ones, being in actuality [[spoiler:the detective Franchise/SherlockHolmes as an anarchist]] in this dark world.
** The detective is one of the only consulting detectives in a fictional Britain named Albion, in a world ruled by {{Eldritch Abomination}}s. When Prince Albert, the nephew of Queen Victoria, is murdered, he takes the case and quickly zeros in on the [[HyperAwareness height and habits of the killers]]. He then tracks the prince's movements using [[MasterOfDisguise an array of disguises]], and quickly realizes Sherry Vernet, the writer of a play the prince loved, is likely his murderer along with an accomplice. When he invites the two of them to a trap later, Vernet reveals he sensed it and has fled. He then deduces that they are only hiding a few miles away, [[ThatsWhatIWouldDo because it's what he would have done.]] [[spoiler: Strongly implied to be Moriarty, it is teased that this will not be the last confrontation between him and Holmes.]]
* NightmareFuel: The narrator's description of his encounter with an EldritchAbomination which maimed him, killed every other soldier present and left him extremely traumatised.