Holmes neatly sums up the whole affair in the final chapter and provides an overview of Stapleton's background and early moves towards gaining the Baskerville estate. Holmes has discovered that Stapleton was Sir Henry's cousin, and that at first he lived in South America. He moved to England eventually, at first running a school, which then failed. So he was left short of money. He found out about the Baskerville estate, however, and moved to Devonshire in order to be close to it while he formulated his plans.
Holmes notes at least three things which indicate that Stapleton planned to gain the estate as soon as he moved to the moor. One is that already at that time he was pretending that his wife was his sister - he evidently had thought already of using her as some kind of 'decoy' (chapter 15). He did indeed go on to use her to try and lure Sir Henry. Holmes also remarks that the very act of establishing himself in the neighbourhood of Baskerville Hall shows that he was scheming to get it. Finally, he made sure of striking up a friendship with Sir Charles, thereby drawing him into his confidence. It was through Sir Charles that he learnt about the family legend of the devilish hound, and concocted an amazingly ingenious plan to use this legend to bring about Sir Charles's demise.
However, Stapleton was then thwarted by Sir Henry turning up from Canada to claim the estate. Holmes observes that he probably had not reckoned with this and at first tried to get rid of him while he was still in London. Failing in this, he then planned to set his fearsome hound upon Sir Henry at Baskerville Hall, just as he had done in the case of Sir Charles.