Helen Stoner has recently been sleeping in the bedroom right next to her stepfather's. This was her sister Julia's room at the time she died under mysterious circumstances. Helen has recently become engaged. Her sister became engaged shortly before she died. Helen hears the same low whistling her sister described...
Helen Stoner has recently been sleeping in the bedroom right next to her stepfather's. This was her sister Julia's room at the time she died under mysterious circumstances. Helen has recently become engaged. Her sister became engaged shortly before she died. Helen hears the same low whistling her sister described to her one night.
“‘Tell me, Helen,’ said she, ‘have you ever heard anyone whistle in the dead of the night? .... Because during the last few nights I have always, about three in the morning, heard a low, clear whistle. I am a light sleeper, and it has awakened me. I cannot tell where it came from—perhaps from the next room, perhaps from the lawn. I thought that I would just ask you whether you had heard it.’"
These are three ways in which Helen Stoner's situation when she visits Sherlock Holmes are similar to Julia's just before she died. Helen is engaged, she is sleeping in the same bedroom, and she has heard the same whistle. It is the whistle that alarms her because it reminds her of what Julia had told her about it earlier. Because of that whistle she waits until daybreak and then hurries to London by dog cart and train to consult Sherlock Holmes. She had gotten his name and address from a friend named Mrs. Farintosh whom the detective had assisted in retrieving a piece of valuable jewelry.
Another thing that Helen and Julia have in common, although this is not found out until much later in the story, is that their stepfather Dr. Grimesby Roylott murdered Julia and plans to murder Helen. The half-mad doctor has thought of sending a poisonous snake through the ventilator into the next-door bedroom, but he can't be sure it will bite the sleeping girl on any given night. He has to have a way of summoning it back up the bell-rope and through the ventilator. So he has trained it to respond to a low whistle which he blows at around three o'clock in the morning while the intended victim is still presumably asleep.
It so happens that Helen is not asleep on the morning she hears the whistle.
Imagine, then, my thrill of terror when last night, as I lay awake, thinking over her terrible fate, I suddenly heard in the silence of the night the low whistle which had been the herald of her own death.
Apparently the only flaw in Dr. Roylott's sinister plan to commit a second perfect crime of murder was the fact that he was forced to blow a whistle at around three o'clock in the morning. When Holmes and Watson are hiding in Helen's bedroom at Stoke Moran, they hear that same whistle, and it leads to Dr. Roylott's death as well as to the solution of the murder of Julia Stoner two years earlier.