Announcing that he cannot glean anything else from the letter, the detective asks Henry whether anything else unusual has happened. Apparently, when Henry put a new pair out to be shined, his boot was lost or stolen. Dismissing the incident, Holmes agrees to fill Henry in on the curse of the Baskervilles. The group debates whether the warning suggests a friend eager to protect the baronet or an enemy intent on scaring him off. Henry announces his intention to go to Baskerville Hall. After inviting the detectives to lunch later that day, he leaves.
As soon as Sir Henry and Mortimer are out the door, Holmes leaps into action, intent on trailing the baronet to spot the letter writer whom Holmes suspects is trailing Sir Henry. Sure enough, the stakeout reveals a suspicious stranger in a cab, but the moment Watson spies his bushy black beard, the villain hurries off. The spy, Holmes suggests, is a worthy rival given his choice of a cab, a supremely well-suited getaway car. Holmes own performance, by contrast, was sub- par: he let the spy know that he was seen. The detective does announce that he has caught the cab's number, 2704, and directs Watson into a nearby messenger office. Once inside, Holmes greets the manager, a former client, and asks for the man's son Cartwright's help. Holmes instructs Cartwright to inspect the garbage of all the hotels in the Charing Cross region, in search of the mutilated Times. Meanwhile, he tells Watson, they will investigate cab number 2704 before meeting Sir Henry for lunch.
In this section, Holmes attacks the case, applying his logical methods to the few clues that they have. His decision to exhaust all real-world options before considering the supernatural is typical of Holmes' style. He decides to rule out all possibilities before he considers that there are supernatural reasons. Ironically, the way that he analyzes clues, and the intuition he uses to gather evidence, is almost supernatural. He is almost superhuman in his keen powers of observation. The book has a very mysterious and dark undertone. These two chapters introduce us to some of the more puzzling clues in the book—the cut-and-paste warning letter, the stolen boot, and the mysterious stranger. In particular, the appearance of the mysterious stranger highlights one of the more prevalent themes in the story: disguised identity. When the detectives spot their man, they cannot help but wonder whether the black beard is a fake. The man's hurried escape ensures that for now, they will not figure out his identity, or whether the beard is a disguise. At the same time, identities and intentions get confused as the detectives wonder whether the stranger and the letter writer are the same person, and whether that person is a friend or an enemy. In this case, a mistaken or uncertain identity adds to the building tension and the tone of mystery in the novel.
Mistaken and disguised identities play a large role in the novel. The villain will continually disguise his own and others' identities. Just like an episode of Scooby Doo, the buildup to the final unmasking, or the revelation of true identities, creates much of the suspense in the story. The conflict between an inexplicable, mysterious, or supernatural identity and a more realistic and logical one, drives the plot of the novel. These two sides: practical and supernatural also represent the different characters' perspectives about Baskerville mystery. Holmes takes a more dogmatic, methodological approach, whereas Mortimer believes in the supernatural explanations.
These chapters also introduce us to the character of Cartwright. Cartwright offers an interesting glimpse into the mindset of upper middle class England during Holmes' time. As an educated person, Holmes expects not only respect, but also service from his social inferiors, and he usually gets it. Cartwright agrees to go rummaging about in the trash for Holmes. Later on, when Holmes and Watson handle an irate cab driver, a few shillings buys him off and ensures his total cooperation. The detectives' interaction with people of lower classes suggests that they do not respect those people whom they consider of a lower social or economic status.