Watson indicates in his introduction to the story that he had made a pledge of secrecy which must have been to Helen Stoner, since she was the only surviving member of the family. It appears that Helen Stoner had recently died. Watson does not specify the cause of her death.
Of all these varied cases, however, I cannot recall any which presented more singular features than that which was associated with the well-known Surrey family of the Roylotts of Stoke Moran. The events in question occurred in the early days of my association with Holmes, when we were sharing rooms as bachelors in Baker Street. It is possible that I might have placed them upon record before, but a promise of secrecy was made at the time, from which I have only been freed during the last month by the untimely death of the lady to whom the pledge was given.
The real author of the story, Arthur Conan Doyle, apparently felt it necessary to date the case back in time in order to explain why Watson should be involved in it from the very beginning. "The Adventure of the Speckled Band" was first published in 1892, but Watson states that Helen Stoner came to Sherlock Holmes at Baker Street in April of 1883, nearly ten years earlier. Helen's back story is so long and involved that Watson would have had to hear it directly from her at the time she consulted Sherlock Holmes; otherwise he would have had no way of relating all the details to his readers. Helen Stoner arrived shortly after seven o'clock in the morning, and the only way Watson could have been there when Holmes received her was if he had still been sharing the rooms at 221B Baker Street with the great detective. So Arthur Conan Doyle simply dated the incidents back to April of 1883 and had Watson explain that he could not publish the case earlier because of his pledge of secrecy, which, of course, would have been made to Helen Stoner after the case was solved and Dr. Roylott was dead.
Conan Doyle also has his narrator Dr. Watson explain that Helen Stoner was extremely concerned about the reputation of the family, including her sister Julia and her stepfather Dr. Roylott, as well as herself. There are at least two examples showing her concern about the family reputation. Sherlock Holmes discovers that she has not told him about the five black-and-blue marks on her wrist which were made by the powerful grip of her violent and half-mad stepfather. And during her long back story she tells Holmes and Watson:
“Last week he hurled the local blacksmith over a parapet into a stream, and it was only by paying over all the money which I could gather together that I was able to avert another public exposure."
This not only characterizes Dr. Roylott as a powerful and violent man, but it helps to characterize Helen as being hypersensitive about protecting the reputation of her family. This hypersensitivity explains why she asked Watson to promise not to tell the true story about the unexplained death of her sister and her stepfather's recent attempt to murder her. The pledge explains why Conan Doyle did not publish the story earlier. He dated the case back to April of 1883 because Watson had to be still living with Sherlock Holmes in order to be in on it from the very beginning.