Helen Stoner tells Holmes that her stepfather is a violent and quarrelsome man.
Helen Stoner comes to see the detective Sherlock Holmes when her sister is killed. She feels that her sister died in suspicious circumstances, and she worries that something might happen to her too. They lived with her stepfather, and the man is not a nice man.
Helen explains to Holmes that her stepfather married their mother, but their mother died and the three of them returned to the family’s estate, Stoke Moran. There he immediately began to fight with the neighbors and generally behave in a horrible manner.
Dr. Roylott suffers from what Helen Stoner refers to as “violence of temper.” He gave up his medical practice and settled into the family estate, but at this time a terrible change came over him.
Instead of making friends and exchanging visits with our neighbours, who had at first been overjoyed to see a Roylott of Stoke Moran back in the old family seat, he shut himself up in his house and seldom came out save to indulge in ferocious quarrels with whoever might cross his path.
Helen has a lot of examples of how her stepfather has been violent and gotten into fights with the neighbors and others. He seems like a perfectly horrible man.
A series of disgraceful brawls took place, two of which ended in the police-court, until at last he became the terror of the village, and the folks would fly at his approach, for he is a man of immense strength, and absolutely uncontrollable in his anger.
It does not seem impossible that someone like this would try to kill his stepdaughters for the inheritance. Dr. Roylott killed one and tried to kill the other. Fortunately, she hired Holmes and he figured out that Roylott was using a snake to commit murder.
Holmes says that when a doctor goes bad, it is the worst thing. Doctors are supposed to help people, not hurt them. However, they are possessed of a great deal of intelligence and cleverness which can be used to commit their crimes, should they go bad.