Holmes is impressed at how Stapleton's so cool under pressure.
Yeah, he's cool—it's not like Holmes can prove any of his ideas in a court of law yet.
(This is just like that Columbo episode where he knows the plumber's lying but—oh, sorry, we digress…)
Holmes believes that Laura Lyons will be the key to this stage of the case.
Watson brings Holmes to Baskerville Hall, and Sir Henry welcomes him.
Watson breaks the news to the Barrymores that Selden's dead.
Holmes tells Sir Henry that he'll soon have the answer to his mystery, as long as Sir Henry does exactly what Holmes says without asking why. More control-freak stuff.
Holmes suddenly jumps up to look at one of the portraits on Sir Henry's wall.
When Holmes points to the portrait of a man in black velvet and lace, Sir Henry identifies him as than Hugo Baskerville—the original victim of the Hound.
After dinner, Holmes leads Watson back over to the portrait.
When Holmes covers Hugo's ridiculous hair, Watson can finally spot what Holmes noticed so long before: that the face of Hugo Baskerville hugely resembles Stapleton's.
In other words, Stapleton must be a member of the Baskerville family.
Sir Henry comes in, and Holmes tells him that he and Watson are planning to go back to London.
Sir Henry's disappointed (and probably scared silly), but Holmes reassures him that they'll be back soon.
They were all supposed to go over to dinner at Stapleton's house together, but now Sir Henry will just have to go alone.
Holmes tells Sir Henry to drive over to Merripit House, but then to have the groom bring the carriage home.
Sir Henry should then tell his host, Stapleton, that he plans to walk home that night.
At the train station in Coombe Tracey, Holmes and Watson meet the boy, Cartwright, who was bringing Holmes' food to the moors over those many days.
Holmes orders Cartwright to take the train into London.
From London, Cartwright should send a telegram to Sir Henry asking about a pocketbook Holmes might have forgotten at Baskerville Hall. (This is all to "prove" that Holmes really is in London. This guy doesn't miss a trick.)
Cartwright agrees, and he also gives Holmes a telegram.
It's from "Lestrade," who's coming down to Devonshire on the 5:40 train with a warrant.
Holmes explains that Lestrade's a policeman, and they may need his help tonight.
Holmes and Watson head over to Laura Lyons' house.
Holmes tells Laura Lyons that he is involved in a case which implicates Stapleton and "his wife" (13.114) in murder.
Holmes shows her pictures of the people now calling themselves Jack and Beryl Stapleton.
The pictures were taken several years ago in York, where they were called Mr. and Mrs. Vandeleur (13.121).
Laura Lyons is shocked that Stapleton has lied to her about his wife. First time in history that's ever happened.
She admits that Stapleton told her what to write in the letter to Sir Charles.
She also says that, after she sent the letter, Stapleton appeared to change his mind about her borrowing money from Sir Charles.
After she agreed not to meet with Sir Charles, she didn't hear anything more about him until she read about his death in the newspaper.
Stapleton then frightened Laura into promising not to say anything about the scheduled appointment with Sir Charles, since his death was so mysterious.
Holmes and Watson go to the train station to meet Lestrade.
Holmes promises that this case is the "biggest thing for years" (13.140).