Doyle's description of the settings of The Sign of the Four rely heavily on imagery to convey the gloom and mood of London. In this passage from Chapter 3, he uses color and light imagery as Watson emphasizes how dismal the city can be:
It was a September evening and not yet seven o'clock, but 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. The yellow glare from the shop-windows streamed out into the steamy, vaporous air and threw a murky, shifting radiance across the crowded thoroughfare.
From the "mud-coloured" sky and streets to the dim pockets of light cast by the street lamps, London emerges from this passage as a foreboding and mysterious environment. In short, London is the quintessential gothic setting, and imagery is a primary device by which Doyle emphasizes the gothic themes of his novel. The physical darkness and gloominess of London itself mirrors the dark and gloomy mood of a novel marked by violence and murder. The sinister setting reinforces the sinister plot and also enhances the suspense for the reader.
The Sign of the Four is the product of colonialism in more ways than one. The narrative revolves around the theft of a vast treasure trove from India, which was under Britain's colonial rule at the time, and Doyle's descriptions of some of his characters are also marked by racist, colonized attitudes toward people of color. In his descriptions of Tonga, in Chapter 10, Doyle relies on metaphorical language of inhumanity and animal rage:
Never have I seen features so deeply marked with all bestiality and cruelty. Hs small eyes glowed and burned with a sombre light, and his thick lips were writhed back from his teeth, which grinned and chattered at us with half animal fury. [...]
I can see the two of them now as they stood, the white man with his legs far apart, shrieking out curses, and the unhallowed dwarf with his hideous face, and his strong yellow teeth gnashing at us in the light of our lantern.
This racist metaphorical language includes the description of Tonga's lips and teeth as writhing, grinning, chattering, and gnashing with "half animal fury" as well as the characterization of his features as "marked with all bestiality." The color and light imagery of Tonga's yellow teeth and glowing eyes also adds to the animalistic description. Through such language, Doyle reduces Tonga to qualities that he identifies with wild animals—and, contrasting Tonga to Jonathan Small, Doyle also demonstrates the racist belief that Black people are less human than white people. This is a particularly blatant instance of Doyle's colonial and imperialist sympathies.
