In chapter 1, Sherlock Holmes meets Dr. Mortimer, who has come to get his assistance with a problem. Holmes shows off his skills in deduction to Watson.
In chapter 2, Dr. Mortimer shares the legend of the hound of the Baskervilles and shares the circumstances of Sir Charles Baskerville's death. Mortimer relates that he personally witnessed "a glimpse of something" that caused Sir Charles to become terrified. Mortimer explains his findings when he examined Sir Charles within an hour of his death--including the footprints of "a gigantic hound."
In chapter 3, Mortimer explains that the new owner of Baskerville Hall, Sir Charles' only known heir, will be arriving in London shortly. Holmes tells Mortimer he will decide within 24 hours whether to take the case. Holmes smokes and considers the case and briefs Watson on some of his theories. He decides to take the case.
In chapter 4, Sir Henry Baskerville and Dr. Mortimer come to call on Holmes. Sir Henry has received a warning note made up of words clipped from the paper. Holmes garners some information from the note via his powers of perception, including that the source of the letter was a London hotel. Sir Henry lets Holmes know that one of his boots was stolen from his hotel room. Holmes suggests Sir Henry may not want to go to Baskerville Hall due to the danger, but Sir Henry insists he will go. Holmes follows Sir Henry after he leaves Holmes' rooms, and he notices a bearded man in a hansom cab trailing the baronet, but they lose him. Holmes sets Watson to the task of tracking down the paper from which the warning note was cut.
In chapter 5, Holmes and Watson pursue three leads in the case and end up empty-handed: They don't find the cut-up newspaper; it turns out Barrymore (the butler) was at home, so he wasn't the spy; and the cabman tells Holmes that the man with the black beard was named Sherlock Holmes. Sir Henry's stolen boot is returned and an old black one goes missing instead. Holmes learns more about the descendants of the Baskervilles to try to identify who might want Sir Henry dead. Holmes assigns Watson to accompany Sir Henry to Baskerville Hall.
In chapter 6, Watson and Sir Henry arrive at Baskerville Hall. They learn there is an escaped murderer named Selden at large. They meet the butler and his wife. Baskerville Hall "isn't a very cheerful place," Sir Henry observes. Watson hears a woman sobbing in the house late at night.