This case is told to Holmes by a woman named Helen Stoner. Holmes and Watson, invite her to share her problem. Miss Stoner tells them that when their mother died Helen and Julia were left in the custody of their stepfather, a dangerous Dr. Grimesby Roylott. They lived in fear and misery, despite of the being wealthy because of money left by their mother. Julia mysteriously died two weeks before her marriage, and before she dies she said to Helen the words ‘speckled band’, but Helen doesn’t have a clue as to the meaning. After two years Helen got engaged, her stepfather approved of it. A renovation of their house forced Helen to sleep in Julia’s room and she heard a whistle. She lit a lamp found nothing, stayed awake and in the morning came to Sherlock Holmes for help. After she told him all her concerns they agreed to meet at her house but she should keep it secret from her stepfather. But she did not know Dr. Roylott followed her and threatened Holmes to back off, after she had left. Worried of Helen’s safety Holmes and Watson came to Stoke Moran and examined the room of Julia and Dr. Roylott. And Holmes noticed some odd things. Holmes asked Helen to signal to him and Watson to come back when Dr. Roylott sleeps. She does this and in the end Holmes and Watson solve the mystery.
Sherlock Holmes calls himself a "consulting detective." Nowadays we might call him a private detective, a private eye, or even a shamus. He is strictly a non-professional, and as such he is limited as to the kinds of cases he can take on. Then as now the police do not want private detectives interfering with murder cases. Holmes is able to get involved in solving murders only because he has done innumerable favors for Scotland Yard detectives and has allowed them to take all the credit for solving many cases he has solved himself. But it should be noted that Holmes rarely gets involved in murder cases before the police have been summoned to the scene of the crime. In the best-known Sherlock Holmes tale "The Hound of the Baskervilles," for example, Holmes is not trying to solve a murder but to prevent a murder. This is strictly legitimate work for a private eye, and many of the Sherlock Holmes stories are about clients who are in danger of being killed but are not actually dead.
In "The Adventure of the Speckled Band," Helen Stoner comes to Holmes for advice. She thinks she might be in mortal danger and is terrified. Holmes goes down to Stoke Moran accompanied by Watson, not to investigate the two-year-old death of Julia Stoner, but to protect Helen. It is noteworthy that he does not even try to arrest Dr. Roylott when he discovers what the vicious man has been up to; instead, the author conveniently arranges for Roylott to be killed by his own snake. Holmes simply does not have the authority to make an arrest. He does not even make the truth about Roylott's swamp adder or about Julia Stoner's death publicly known. Dr. Watson explains in the opening paragraph that the whole thing has been kept secret until he is currently revealing the truth in this story he entitles "The Adventure of the Speckled Band."
It is possible that I might have placed them upon record before, but a promise of secrecy was made at the time, from which I have only been freed during the last month by the untimely death of the lady to whom the pledge was given. It is perhaps as well that the facts should now come to light, for I have reasons to know that there are widespread rumours as to the death of Dr. Grimesby Roylott which tend to make the matter even more terrible than the truth.