How does the setting change as watson sir henry and dr mortimer travel to baskerville hall? chapter 6

On their way to Baskerville Hall, they meet a man guarding part of the moor. The moor has an ominous mood to it. Apparently, a convict had escaped three days earlier from the prison at nearby Princetown. This convict's name is Selden, and he is known as the Notting Hill murderer. Watson recalls Sherlock's interest in that case because of the criminal's brutality, and imagines Selden hiding out on the moor.