Chapter 4 of “The Hound of the Baskervilles” begins with Dr. Mortimer visiting 221B Baker Street to meet with Sherlock Holmes and Dr. Watson. Mortimer informs them about the legend of the hound and his concern that the Baskervilles curse is still active.

He also states that Sir Charles Baskerville got a warning letter before his death, cautioning him to avoid the moor. Holmes becomes interested in the matter and asks Mortimer to bring Sir Henry Baskerville, Sir Charles’ heir, to meet him.

Meanwhile, Watson pursues Sir Henry, who has arrived in London from Canada, to his hotel, where they become acquainted. Watson is attracted by Sir Henry’s charisma and ambition to unravel the mystery of his family curse. Later, Watson and Sir Henry are joined by Holmes, who has come to meet them. Holmes tells Sir Henry to be cautious while staying at Baskerville Hall and suggests Watson accompany him as a companion.

The chapter concludes with Sir Henry getting another warning letter, similar to the one Sir Charles got, confirming that the family curse is more than just a legend, but a genuine menace.