They come face to face in chapter 14 of 'The Hound of the Baskervilles.'
Watson and Sir Henry dine there the night of their arrival in Chapter 6
The reason the hound attacked Selden was that he was wearing the clothes that Sir Henry had given Barrymore. Barrymore turned and gave them to Selden. Stapleton had set the hound on the scent of Sir Henry, and since the hound smelled the scent of Sir Henry, it attacked Selden.
Sir Henry Baskerville is Sir Charles Baskerville's nephew.
The climax of the story would probably be when the hound lurks from the shadows to chase Sir Henry Baskerville.
Holmes and Watson find a body in the darkness of night dressed in Sir Henry's clothes, but it turns out to be Selden in the clothes that Sir Henry had given to the Barrymores just days earlier.
In Chapter 12 of "The Hound of the Baskervilles," Sherlock Holmes is hiding to gather intelligence and observe events without being detected. He wants to confirm his suspicions about Sir Henry Baskerville and the mysterious occurrences surrounding the Baskerville estate. By remaining concealed, Holmes can investigate the situation more effectively and protect his client while unraveling the truth behind the legendary hound.
"On the death of Sir Charles we inquired for this young gentleman [Sir Henry Baskerville], and found that he had been farming in Canada." -- Dr. Mortimer, 'The Hound of the Baskervilles
In "The Hound of the Baskervilles," the composer of the letter, which is ultimately revealed to be forged, attempts to conceal the true nature of the threat against Sir Henry Baskerville. The letter implies a warning about danger related to the moor and the Baskerville curse, aiming to instill fear and manipulate Sir Henry's actions. This deception is part of a larger plot to control events surrounding the Baskerville estate and eliminate Sir Henry. Ultimately, the letter's intent is to create confusion and steer Sir Henry away from the truth of the situation.
No!! Sherlock Holmes had nothing to do with the romance in the Hound. It was only between Sir Henry and Beryl Stapleton.
Because she was really Stapleton's wife
Sir Henry Baskerville himself raises the issue of the missing boot at the hotel.
In Chapter 6 of "The Hound of the Baskervilles," Sherlock Holmes instructs Dr. John Watson to accompany Sir Henry Baskerville to Baskerville Hall and observe the situation closely. He emphasizes the importance of gathering information and being vigilant about any unusual occurrences. Holmes expresses his intent to conduct his own investigations separately, indicating that he trusts Watson to keep a watchful eye on events as they unfold.