Holmes and Watson take Toby back to the point where he had got confused, attempting to regain the trail. This leads them to a small boatyard by the river. A sign advertises “boats to hire by the hour or day” by someone named Mordecai Smith. Holmes feels that “these fellows are sharper than I expected.”
This sets up the dramatic boat chase of the penultimate chapter. It also provides a further challenge to Holmes’ intellect.
Holmes speaks with a woman in the doorway of a nearby house, who is trying to get her young son inside for a wash. By pretending that he wants to hire a boat, Holmes gleans from her that Mordecai Smith has gone off somewhere in his steam launch, hired by a man with a wooden leg. He tricks her into revealing the name and appearance of the steam launch: the black, red-streaked Aurora.
The woman is Mordecai’s wife, and is presented as working-class and distinctly unsavvy, as Holmes tricks her with ease. This is in keeping with general narrative of Holmes as a superior mind.
Holmes thanks the woman and goes off with Watson, explaining that “the main thing with people of that sort is never to let them think their information can be of the slightest importance to you.” Holmes decides that the best course of action is to employ a gang of street urchins known as the Baker Street Irregulars and sends a telegram to their “lieutenant” on the way home.
Holmes’ pithy statements to Watson are quite often the kind of thing that contemporary readers would find uncomfortable and inaccurate. Here, he essentially pegs the entire working class as distrustful, suggesting that they are little more than accessories.
Back at the flat, Watson takes some much-needed respite by having a bath. When he gets out, Holmes shows him an article in the paper talking about the case and praising Athelney Jones’ detective work—much to Holmes’ amusement.
Jones’ misguided attempts to solve the case amuse Holmes, rather than hinder him, because he knows eventually it will be him that reveals the truth. This is part of the thrill he gets from the cases.
The Baker Street Irregulars arrive. Holmes explains that he wants them to track down the whereabouts of the Aurora by spreading out among London’s various docks. In exchange, he will pay them a shilling each per day. They hurry off to work.
The Baker Street Irregulars are another part of Holmes’ extended network, essentially helping him to have eyes and ears in more than one place at a time.
Watson asks Holmes if he intends to sleep. Holmes says that he is not tired; only “idleness” tires him. Instead, he will spend some time thinking about the identity of the accomplice with the small footprints. Watson exclaims that the small footprints and the blow darts point towards a “savage,” perhaps from South America.
Holmes functions differently from ordinary people and, with the case functioning like a stimulating drug, he doesn’t need sleep while he is under its influence. The link between the accomplice and the “savage” foreigner becomes clear, setting Tonga up as the true embodiment of evil and fear in the novel (whereas Small’s actions will be characterized as misguided but understandable).
Holmes consults a book and finds an entry on “the aborigines of the Andaman Islands.” This says that they are perhaps the “smallest race upon this earth,” and are “fierce, morose, and intractable people.” It describes their appearance as “naturally hideous, having large, misshapen heads, small fierce eyes and distorted features.” Holmes reasons that this is the likely identity of the accomplice. He instructs Watson to get some rest, playing him to sleep with his violin.
The Andamanese are a real tribe or, more accurately, a combination of tribes that still exist on the islands today. Doyle completely buys into the Victorian fear of the foreign “other,” implying the tribespeople to be irrational, inferior, and evil. British colonial exploits in nearby India had a destabilizing effect on the Andaman Islands, introducing Eurasian diseases that were new to the area. Holmes’ sudden switch to playing the violin is an unsubtle move from undeveloped savagery to the high culture of Western society.