About a month later, Holmes and Watson are sitting by the fire in their apartment in London.
They've had a visit from Sir Henry and Dr. Mortimer, who are about to go on a relaxing trip around the world to help improve Sir Henry's "shattered nerves" (15.1). No kidding.
Since the case of the Baskervilles is on Watson's mind, he presses Holmes to tell him more about the background of the case.
Apparently, Mrs. Stapleton has confirmed Holmes' guess that Stapleton was a Baskerville.
He was the son of Rodger Baskerville, Sir Charles' younger brother, who moved to South America to escape some nasty rumors about him.
Stapleton's real name was Rodger Baskerville (Junior, we guess?), and he married a South American woman named Beryl Garcia.
He and Beryl came to England under the fake name of Vandelay—wait, we meant Vandeleur—after running away with some embezzled money.
They opened a school, which eventually failed.
So the Vandeleurs changed their names to Stapleton and moved to the south of England.
Stapleton discovered that he was pretty close to being the heir to the Baskerville fortune.
And—luckily for him, because he was a creep—the current holder of that fortune (Sir Charles) was easily frightened and had a heart problem.
So Stapleton bought a giant dog, mixed up some phosphorus, plunked the dog down in the middle of the Grimpen Mire, and waited for his chance.
Stapleton had planned at first to live with Beryl as his sister rather than his wife just in case he could use her to attract Sir Charles.
But she absolutely refused to help Stapleton in this way.
Stapleton lucked out when he met Laura Lyons, whom he manipulated into writing to Sir Charles for help in getting a divorce.
On the night of Sir Charles' death, Stapleton brought the dog to the driveway where Sir Charles was waiting for Laura.
Stapleton released the dog on Sir Charles, who ran away screaming until he collapsed from his weak heart.
That's why there was a paw print near Sir Charles' body.
Both Beryl and Laura Lyons suspected Stapleton of planning Sir Charles' death, but neither would turn on him while they were still in love with him.
And then, along came Sir Henry.
Stapleton traveled to London to see if he could figure out some way of stopping Sir Henry from coming down to Baskerville Hall at all.
At this point, Stapleton had stopped trusting Beryl, so he dragged her along on the trip and kept her prisoner in the hotel while he spied on Sir Henry. (Keeping women locked up seems to run in the Baskerville family.)
She still managed to send Sir Henry her secret message cut out of the Times, though.
The disappearing boots were also a clue: the first one was too new to smell like Sir Henry, which is why Stapleton returned it.
The older black boot was better for training his giant dog to chase the scent.
When Stapleton spotted Holmes in the company of Sir Henry, he realized that there was no point in continuing to hunt Sir Henry in London.
Stapleton went back to Merripit House with his wife to try his luck in Dartmoor.
Even before Holmes went down to the moors, he already suspected Stapleton.
The problem was catching him, with enough proof to make a legal case against him.
That's why Holmes set up poor Sir Henry as bait to catch Stapleton red-handed.
As for Beryl, she started out helping Stapleton because she really loved him (and feared him).
But as time went on, Beryl's loyalties shifted to Sir Henry and she began to hate Stapleton.
Finally, on the night of the attack, Beryl tried to stop Stapleton from setting up Sir Henry for death-by-dog, and he tied her up to keep her out of the way.
So that's that.
There's nothing more that Holmes can say with any certainty.
So he and Watson go off to the opera for the evening—a happy ending (except for all the deaths, of course).