In Sir Arthur Conan Doyle's The Adventure of the Speckled Band, when the truth about Miss Julia Stone's death is revealed, it affects the characters in different ways. In what ways does this truth affect both Holmes and Miss Helen Stone?
In Sir Arthur Conan Doyle's The Adventure of the Speckled Band, we are not directly told Ms. Helen Stone's reaction to learning the true means by which her twin sister Julia died; however, we can infer her reaction. She is very much afraid of her stepfather and was under the impression that he would be in London while Sherlock Holmes performs his investigation. So, when Sherlock informs her that he and Watson met her stepfather, Dr. Roylott, she grows ashen white when she figures out he had followed her to London where she had her appointment with Mr. Holmes. Hence, we can deduce that when Helen learns her sister was killed by a poisonous snake their stepfather sent into Julia's room, we can be sure that Helen is very relieved. She would especially be relieved to learn that the snake has, ironically, now even killed her stepfather. Now that she no longer has to worry about him threatening her life, she can happily marry and claim her mother's money. Though, of course, she is still sad to learn of how her sister has been murdered by their stepfather.
We first see Holmes's reaction when, in the dark with Watson, he hears what he knows to be the snake hissing in the ventilator, a reaction that is both terrified and able to act. As Watson describes, Holmes "lashed furiously with his cane at the bell-pull." What's more, Watson describes that Holmes's face, as he whacked at the bell-pull, was "deadly pale and filled with horror" because Holmes has figured out prior to this point that they are fighting against a poisonous snake let loose by Helen's stepfather. His reaction changes once he hears what he knows to be the stepfather crying out in pain, because now he knows what has happened to the snake. His reaction as he enters Dr. Roylott's room is "grave," meaning serious, and even philosophical as he reflects on the justice in the fact that Dr. Roylott has just been killed through the violent scheme he had killed Julia with and now planned to kill Helen with. He then very calmly captures the snake and puts it back in its iron safe. Later, he confesses to Watson that he must have struck the snake with his cane when it entered their dark room, which drove it back to its master's room, making it angry enough to attack the "first person it saw," which was his master. Holmes concludes by saying, "In this way I am no doubt indirectly responsible for Dr. Grimesby Roylott's death, and I cannot say that it is likely to weigh very heavily upon my conscience."
Hence, Helen's reaction to learning of her father's murderous actions was one of relief and also sadness. Holmes's reaction was first fear for his and Watson's own life, then a feeling of philosophical satisfaction at learning the snake had killed the stepfather instead.