How does Conan Doyle present London as a mysterious and sinister setting for a mystery in The Sign of Four?
In this second Sherlock Holmes novel, Arthur Conan Doyle uses various locations in and near central London as a setting for a two-fold mystery: what happened to Captain Morstan, and who has been sending his daughter, Mary, a pearl each year since his disappearance.
In Chapter Three, "In Quest of a Solution," Watson describes the London streets Holmes, Watson, and Miss Morstan pass through:
"The yellow glare from the shop-windows streamed out into the steamy, vaporous air, and threw a murky, shifting radiance across the crowded thoroughfare. There was, to my mind, something eerie and ghost-like in the endless procession of faces which flitted across these narrow bars of light,—sad faces and glad, haggard and merry... I am not subject to impressions, but the dull, heavy evening, with the strange business upon which we were engaged, combined to make me nervous and depressed."
Here, Doyle uses the gloom of the city on this September evening to deepen the unease that Watson feels; Holmes has pocketed a small revolver before setting out "to an unknown place, on an unknown errand." The trio are made to switch cabs halfway through their journey and glimpse the "broad, silent water" of the Thames before reaching "a questionable and forbidding neighborhood" where they encounter Thaddeus Sholto in his home "in the howling desert of South London," a newly finished and dimly-lighted home in a block of uninhabited terrace houses.
The South London home of Thaddeus's brother, Bartholomew, is forbidding; Pondicherry Lodge is described as having "a very high stone wall topped with broken glass" and "a single narrow iron-clamped door formed the only means of entrance."
Besides the sense of foreboding accomplished with the mysterious trips through sordid London streets to the homes of the Sholto brothers, in chapter seven,"The Episode of the Barrel," Watson describes his journey to the Pinchin Lane taxidermist, Sherman, as moving through "silent gas-lit streets" to his house with live and stuffed animals.
Conan Doyle presents London as shrouded in fog and mystery in The Sign of Four. As Holmes and Watson drive to the Lyceum Theatre in Chapter 3 with Mary Morstan, they are surrounded by fog:
"The day had been a dreary one, and a dense drizzly fog lay low upon the great city. Mud-coloured clouds drooped sadly over the muddy streets. Down the Strand the lamps were but misty splotches of diffused light which threw a feeble circular glimmer upon the slimy pavement."
London is dreary, and the light in this type of weather is refracted in strange ways. Watson says about people in this type of light: "they flitted from the gloom into the light and so back into the gloom once more," and he says this movement from the gloom back to the light is "like all mankind."
This is a fitting setting for a mystery in which characters are cast into the darkness of doubt and then removed into the light of innocence, and vice versa. The setting in London, alternating between gloom and light, is also a metaphor for Holmes's moods, as he alternates between gloomy depression, when he takes cocaine and morphine, and periods of great energy, when he is solving mysteries.