In "The Adventure of the Speckled Band," why has Helen come to talk to Holmes?
From a purely practical perspective, the author had to have Helen come to see Sherlock Holmes at his Baker Street flat because that was the only way he could become involved in the case. Many of his cases begin with someone coming to him for advice or assistance. Jabez Wilson of "The Adventure of the Red-headed League" is another example. It is really hard to believe that a man would come to Holmes because of that business with the Red-headed League, but Holmes had to get involved in the situation somehow. These are the kinds of plot problems Doyle always had to cope with, especially when they involved very little in the way of remuneration. Ostensibly, Helen comes to Holmes because she is terribly frightened and still mystified by the strange death of her sister. The initial interview is short and unproductive. She lives at a great distance away. Holmes' involvement with her problem seems hard for the reader to accept.
Helen has always been wary of the way her twin sister Julia died. Julia died right before her wedding and now with her own nuptials not to far away Helen begins to notice some of the same things that Julia had told her about....the whistle and clang in the dead of night. She has also been made to sleep in Julia's old room. Holmes had helped a friend of Helen's and she didn't know where else to turn.
Helen came to talk to Holmes because she is afraid. She is afraid of the general situation in which she lives (wild animals roving around). She is also afraid more specifically for her life, because her sister Julia died there.