A great many of the Sherlock Holmes stories turn out to be about money, even though the mercenary motif is not visible at the beginning. Some examples are "The Speckled Band," "The Solitary Cyclist," "The Blue Carbuncle," and "The Red-Headed League." "The Hound of the Baskervilles" appears to be a story about the supernatural, a subject in which Sir Arthur Conan Doyle was keenly interested. However, it turns out that one of Sir Henry Baskerville's neighbors, Mr. Stapleton, is exploiting an old legend about a gigantic mythical hound to kill off the two men who are ahead of him in line of succession to the Baskerville estate. Stapleton keeps a vicious hound in a secret place and has used it already to cause the death of Sir Charles Baskerville of an apparent heart attack. Stapleton occasionally allows the hound to run free at night in order to terrify everyone in the region and to perpetuate the legend that there is indeed a ghost-hound that haunts the moors. If Stapleton can succeed in having his hound kill Sir Henry, he will be able to claim the Baskerville estate. However, he cannot expect a young man like Sir Henry to die of a heart attack upon seeing the hound painted with phosphorous. The hound will have to kill this victim, and Stapleton would of course be guilty of premeditated murder.
As is characteristic of most Sherlock Holmes stories, the great detective explains many of the essential details to his friend and biographer at the end. In Chapter XV, "A Retrospection," Holmes tells Watson:
“My inquiries show beyond all question that the family portrait did not lie, and that this fellow [Stapleton] was indeed a Baskerville. He was a son of that Rodger Baskerville, the younger brother of Sir Charles, who fled with a sinister reputation to South America, where he was said to have died unmarried. He did, as a matter of fact, marry, and had one child, this fellow, whose real name is the same as his father."
In Sherlock Holmes' novel The Hound of the Baskervilles, the main elements of the mystery lie around the motives for the murder and the identity of the murderer. As with many of Doyle's works about Holmes, a major theme is scientific and rational explanations of things which on their surface might appear supernatural.
The opening of The Hound of the Baskervilles describes at some length the mysterious curse surrounding the Baskerville family, and the supernatural hound associated with it. The piece of family history that turns out most important though, has nothing to do with the supernatural, but has to do with a more practical aspect of family history.
Stapleton turns out to be third in line to inherit the vast wealth of the Baskerville family, as mentioned above. After he kills Sir Charles, only Sir Henry remains between him and the estate. Stapleton takes advantage of local superstitions by making a large and vicious dog appear to be the mythic hound by coating its muzzle with phosphorus. Eventually, behind the murders lies not a mysterious curse but simple human greed.
He killed sir charles and tries to kill sir henry baskerville because so he could solely inherit the baskerville estate and its immnense wealth.........................................
In Ch.3 Dr.Mortimer the executor of Sir Charles Baskerville's will gives us the history of the Baskerville family. Sir Charles Baskerville the murder victim is the eldest of the three Baskerville brothers. "The second brother, who died young, is the father of Henry. The third, Rodger, was the black sheep of the family." Rodger "fled to Central America and died there in 1876." Rodger was believed to have died unmarried.
However, in Ch.14 Holmes reveals that Rodger did indeed marry and had a son. Stapleton is this son. So, first Stapleton kills Sir Charles Baskerville and then attempts to kill Sir Henry, "the last of the old race, and the heir to great wealth" so that he could solely inherit the Baskerville Estate and its immense wealth. Fortunately, Holmes saves Sir Henry's life at the nick of time.