Doyle's style is highly literary—he lavishes the reader with vivid descriptions of the novel's various set-pieces, and Holmes's own reasoning often takes place in lengthy and stylized diatribes that emphasize the detective's quirky style of thinking.
The introduction of Mary Morstan, in Chapter 2, is excellent evidence of the occasional wordiness of Doyle's style:
Miss Morstan entered the room with a firm step and an outward composure of manner. She was a blonde young lady, small, dainty, well gloved, and dressed in the most perfect taste. There was, however, a plainness and simplicity about her costume which bore with it a suggestion of limited means. The dress was a sombre greyish beige, untrimmed and unbraided, and she wore a small turban of the same dull hue, relieved only by a suspicion of a white feather in the side. Her face had neither regularity of feature nor beauty of complexion, but her expression was sweet and amiable, and her large blue eyes were singularly spiritual and sympathetic. [...]
And so the description continues. As evident in this passage, Doyle's writing tends toward rich visual description—with a special attention to color, as with the "white feather" and Morstan's "dull," "beige" outfit—and a sensitivity to how a character's demeanor might reflect on their visage. This is fitting given that the book's protagonist, Sherlock Holmes, is a detective who is famously able to solve difficult cases because he notices easily overlooked details. With highly descriptive passages like this, Doyle implicitly encourages the reader to devote the same close attention to the characters, as anything and everything could be a potential clue to solving the mystery at the heart of The Sign of the Four.
In Doyle's description of the world around his characters, his language is no less evocative. In Chapter 3, he describes the city of London as a sort of monster:
We had indeed reached a questionable and forbidding neighbourhood. Long lines of dull brick houses were only relieved by the coarse glare and tawdry brilliancy of public-houses at the corner. Then came rows of two-storeyed villas, each with a fronting of miniature garden, and then again interminable lines of new, staring brick buildings—the monster tentacles which the giant city was throwing out into the country.
Through a variety of literary devices, oftentimes strung together in succession, Doyle ensures that all parts of his novel's world come to life before his reader in service of the narrative's dark, suspenseful ambience.
