What is the central conflict in "The Adventure of the Speckled Band" by Sir Arthur Conan Doyle, and how is it resolved?

The central conflict in "The Adventure of the Speckled Band" is whether Helen Stoner will be murdered. Questions raised include: What caused the mysterious death of Helen Stoner's sister two years before? Has she been murdered by the young woman's evil stepfather, Dr. Grimesby Roylott? If so, is Helen, as she suspects, next on the list?
Holmes takes on Helen's case, and the conflict is resolved through Holmes's use of rigorous logic and a process of deduction. At Stoke Moran, the family manor, Holmes does a careful hands-on survey of the estate, especially of the bedroom wing where Helen has been forced to move to her sister's old room. He discovers several things about the room that are odd: a bed that is "clamped" to the floor, a rope to ring a bell to call a servant that is not hooked up, and a hole in the wall between Helen's room and Dr. Roylott's. Holmes and Watson take the hands-on investigation further when they spend a night in Helen's room and a poisonous snake comes through the small hole between the rooms and shimmies down the bell rope, sent there by Dr. Roylott to bite and kill Helen. The snake, chased away by Holmes, instead bites and kills Roylott.
Holmes explains at the end that he was at first confused by the sister's words about the speckled band, which she cried out as she died. Holmes thought that it referred to the band of gypsies living nearby. But when he realized nobody could enter the bedroom, he realized "band" must refer to a snake.
As is often the case in murder mysteries, the central issue is money. Both young women were due to receive a portion of their mother's money on marriage and Dr. Roylott wanted to prevent that.

The central conflict in "The Adventure of the Speckled Band" is that a young woman, Helen Stoner, fears that her stepfather, Dr. Grimesby Roylott, is trying to kill her, but she is unable to prove it. She comes to the office of Holmes and Watson in the hope that they will investigate the mysterious death of her twin sister and determine whether she, too, should fear for her life.
Dr. Grimesby Roylott attempts to intervene and visits Holmes himself, telling him to stay out of their lives. Holmes ignores the threat and begins his investigation with a look at Helen's mother's will.
Ultimately, it turns out that Roylott has indeed killed Helen's sister and is laying plans to murder her in the same way, by forcing a venomous snake into her room as she lies sleeping. His motive is money: his deceased wife has left two-thirds of her legacy to her daughters upon their marriages, and so Roylott attempts to prevent their inheritance by killing them before they have a chance to marry.