'There are still something I don't understand,' I said to Holmes. ' Tell me - who was Stapleton? Why want to kill Sir Henry?'
'It is simple, my dear Watson,' said Holmes. 'Remember Sir Charles had two brothers. The youngest brother, Roger, was a bad man. He got into trouble over money and went to
South America. He died in Venezuela. He did not marry, so no one knew he had a son.'
'And this son called himself Stapleton?'
'Yes, and the son was both bad and clever. He wanted the Baskerville money. There were only two Baskervilles left alive - Sir Charles and Sir Henry. If they died, Baskerville Hall would belong to Stapleton.'
'What about his wife? Why did Stapleton say she was his sister?'
'At first, Stapleton wanted her marry Sir Charles or Sir Herny. That was way of getting the money.'