What three clues are the most important in the plot of "The Adventure of the Speckled Band? Explain the significance of each.
"The Adventure of the Speckled Band" is an example of a so-called "locked-room murder mystery." The biggest question is: "How could Julia Stoner have been murdered in her bedroom with her door locked and the window tightly shuttered?" The prototype for this story was probably Edgar Allan Poe's "The Murders in the Rue Morgue," in which the question was how two women could have been murdered in a room in which their door and windows were tightly shut. The door or one of the windows might have been open when the murderer entered, but how could he exit and leave door and windows locked from the inside?
Holmes is trying save his client Helen Stoner from being murdered, but this automatically involves trying to find out how her sister was murdered two years earlier in the same room with the door locked and shutters bolted. The three most important clues have to be found inside that room. They are the ventilator between Helen's and her stepfather's rooms, the dummy bell-rope, and the fact that the bed is held in one place by being clamped to the floor. After the mystery has been solved and Dr. Roylott is dead, Holmes explains to Watson what he deduced from these three clues.
"My attention was speedily drawn, as I have already remarked to you, to this ventilator, and to the bell-rope which hung down to the bed. The discovery that this was a dummy, and that the bed was clamped to the floor, instantly gave rise to the suspicion that the rope was there as a bridge for something passing through the hole and coming to the bed. The idea of a snake instantly occurred to me, and when I coupled it with my knowledge that the doctor was furnished with a supply of creatures from India, I felt that I was probably on the right track."
Note that this is the first time the word "snake" is used in the story. The author, Sir Arthur Conan Doyle, knew that the word could give away his whole plot if he used it earlier. The reader would guess that a snake could get into the locked room even if it were impenetrable by a human murderer. That is why the term "speckled band" is used in the text and even in the title up to the point where the trick has been exposed. Holmes' deductions are put to the proof when he and Watson spend the night in Helen's room and the snake is plainly seen by both men at around three o'clock in the morning.
It would seem that Julia Stoner must have seen the snake after she had been bitten two years ago. The reason she doesn't call it a snake but a "speckled band" is that she is dying from the fast-acting venom and is nearly in a coma already. When Helen is describing that night to Holmes at Baker Street early that morning, she tells him her sister's last words:
"'Oh, my God! Helen! It was the band! The speckled band!’ There was something else which she would fain have said, and she stabbed with her finger into the air in the direction of the doctor's room, but a fresh convulsion seized her and choked her words."
Julia was trying to tell Helen that she had been bitten by a snake and to indicate that their stepfather was responsible. But Helen still doesn't understand this at the time of her early-morning interview with Holmes. When he asks her what she thinks her sister meant, she tells him:
“Sometimes I have thought that it was merely the wild talk of delirium, sometimes that it may have referred to some band of people, perhaps to these very gipsies in the plantation. I do not know whether the spotted handkerchiefs which so many of them wear over their heads might have suggested the strange adjective which she used.”
The author is obviously trying to preserve his mystery until the climax, when Holmes lights a candle and whips the snake with his cane, driving it back up the dummy bell-rope and through the ventilator, where it bites Dr. Roylott and kills him.