What kind of an atmosphere is created by the author of the play script in the first scene, what does the opening signify?

The first mystery (or, the mystery-within-the-mystery) is the identity of Porlock and what Moriarty might be up to. It has been suggested Porlock was actually Mycroft, Sherlock Holmes’s elder brother, but Doyle never stated this definitively. Porlock is shadowed in mystery and fear, and his connection to that most cunning of Holmes’s enemies, Moriarty, is also ambiguous. Moriarty never makes an actual appearance in the novel; instead, he is fashioned through the comments of Holmes and MacDonald; this adds to the character’s mystique, especially as it becomes clear that, without nearly any evidence, he is indelibly connected to this case.