Definition of Allusion
In the first part of the story, Watson recounts being hit by flashbacks of his former life as he passes the door of the building he used to live in with Holmes. Knowing that Holmes still lives there, he feels inclined to pass through that door again and thereby reenter his life as Holmes's friend and sidekick. To capture this nostalgia, he alludes to an earlier Sherlock Holmes novel, A Study in Scarlet:
As I passed the well-remembered door, which must always be associated in my mind with my wooing, and with the dark incidents of the Study in Scarlet, I was seized with a keen desire to see Holmes again, and to know how he was employing his extraordinary powers.
In the first part, Watson attempts to slip out just as the King of Bohemia is about to arrive. Holmes instructs him to stick around, however. Making an allusion to a historical figure, Holmes states that he requires Watson's presence:
Unlock with LitCharts A+Stay where you are. I am lost without my Boswell. And this promises to be interesting. It would be a pity to miss it.
When the King of Bohemia enters Holmes's apartment in the story's first part, Watson describes his appearance in detail. Combining rich visual imagery with allusion, Doyle develops the character as an imposing, yet also ostentatious and naive, member of the uppermost elite:
Unlock with LitCharts A+A man entered who could hardly have been less than six feet six inches in height, with the chest and limbs of a Hercules.
In the second part of the story, Watson witnesses Holmes in disguise on two separate occasions. The first time, he has to look three times before feeling "certain that it was indeed he." The second time, he uses allusion to describe how much he admires Holmes's extraordinary talent for disguising himself:
Unlock with LitCharts A+His broad black hat, his baggy trousers, his white tie, his sympathetic smile, and general look of peering and benevolent curiosity were such as Mr. John Hare alone could have equalled.