Three ways in which Helen's present situation is similar to that of her sister Julia just before she died are to be found in Helen's long back-story to Sherlock Holmes when she comes to consult him at 221B Baker Street. In the first place Julia was engaged to be married.
We had, however, an aunt, my mother's maiden sister, Miss Honoria Westphail, who lives near Harrow, and we were occasionally allowed to pay short visits at this lady's house. Julia went there at Christmas two years ago, and met there a half-pay major of marines, to whom she became engaged.
Now Helen has recently become engaged herself.
A month ago, however, a dear friend, whom I have known for many years, has done me the honour to ask my hand in marriage. His name is Armitage—Percy Armitage—the second son of Mr. Armitage, of Crane Water, near Reading.
Julia had heard a low whistle on three consecutive nights before the night on which she met her death. Julia asks Helen if she has ever heard it. Helen had not heard it because her bedroom was farther away from Dr. Roylott's room, on the opposite side of Julia's. Julia asks about it, as she says,
“‘Because during the last few nights I have always, about three in the morning, heard a low, clear whistle.'"
On the night before Helen rushes to consult Sherlock Holmes, she hears the same low whistle for the first time.
"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."
The third way in which Helen's situation is now similar to that of Julia just before she died is that now Helen is sleeping in Julia's room and sleeping in Julia's former bed.
"Two days ago some repairs were started in the west wing of the building, and my bedroom wall has been pierced, so that I have had to move into the chamber in which my sister died, and to sleep in the very bed in which she slept."
When Holmes and Watson go down to Stoke Moran to inspect the premises, Holmes tells Helen:
"By the way, there does not seem to be any very pressing need for repairs at that end wall.”
She is already aware of that fact. She replies:
“There were none. I believe that it was an excuse to move me from my room.”
Dr. Roylott killed Julia two years ago by sending a poisonous snake through the ventilator between their adjoining rooms. The snake climbed down the dummy bell-pull and right onto Julia's bed. The snake was either on the bed beside the sleeping girl or possibly even under the covers beside her for the three nights during which she was not bitten. It was evidently on the fourth night that Julia did something in her sleep to aggravate the snake and was fatally bitten. Helen was not engaged to be married at that time, but when she became engaged her stepfather created an excuse to move her into Julia's former bedroom so that he could murder her in the same way he had murdered her sister. He had trained the snake to return through the ventilator when he blew softly on a whistle. He always summoned the snake back at around three o'clock in the morning, because he did not want the sleeping girl to wake up and find a snake in her bed, and he assumed that if the snake hadn't bitten her by that time it wasn't going to bite her that night. The doctor had to wait four nights before the snake finally bit Julia. Helen tells Holmes that on the night of Julia's death they found the charred stump of a match in her right hand and a match-box in her left. It would appear that she had rolled over in bed to reach for the match-box and rolled right on top of the snake which was curled up under the covers beside her for warmth. The snake was only in Helen's bed one night. She heard the same low whistle her sister had described to her two years earlier, and the terrified girl came to see Sherlock Holmes as soon as there was enough daylight. In both instances, Dr. Roylott wanted to murder his stepdaughters because they had become engaged and he was legally obligated to give them large annual payments from his deceased wife's capital under the terms of her will if and when they married.