The Question and Answer section for The Hound of the Baskervilles is a great resource to ask questions, find answers, and discuss the novel.
Holmes doesn't follow Stapleton into the mire to arrreat him because it would be a waste of time to go there at night.
See," said he. "No one could find his way into the Grimpen Mire to-night."
I'm not exactly sure what you are referring to here. Can you be more specific about your question?
Holmes was fascinated with the portrait because it bore a striking resemblance to Stapleton.