Helen Stoner is a fictional character from the Sherlock Holmes story "The Adventure of the Speckled Band," written by Arthur Conan Doyle. She is the daughter of the late Dr. Grimesby Roylott and seeks the help of Sherlock Holmes to investigate the mysterious circumstances surrounding her sister's death. In the story, Helen lives in a large, decaying estate called Stoke Moran with her stepfather, who is known for his violent temper. Helen's fear of her stepfather and the strange occurrences in the house lead her to seek Holmes's expertise, making her a key figure in the unfolding mystery.