How does Doyle use mood, setting, and tone to make the novel more interesting? (chapter 15)

Doyle utilises all of these to establish mystery and the threat of danger. There are a lot of examples to choose from. Consider, for example, the creepy moor. Could there actually be a hellhound there? Doyle describes it with words like "gray", "melancholy" "dim" and "vague". These words not only describe the moor but function as adjectives for the story as a whole.