The Adventure of the Speckled Band by Sir Arthur Conan Doyle is a story in which Sherlock Holmes and his faithful chronicler Watson come to the help of Helen Stoner. Several clues are presented along the way that help Holmes solve the mystery.
First, we have Helen's sister's dying words, "the speckled band." Next, we have the will of Helen's mother, which shows that Roylston will benefit from the sisters' death.
When Holmes arrives at Stoke Moran, he discovers three more clues, the bed anchored to the floor, what appears to be a nonfunctional bell pull, and a small hole that leads between Helen's bedroom and that of Roylston. Another clue is the insistence of Roylston that the young women must sleep in that specific bedroom, despite the fact that Helen is naturally reluctant to sleep in the room where her sister died.