At the end of "The Adventure of the Speckled Band," the mood is both serious and reflective. It is serious because Holmes admits his part in causing the death of Dr Grimesby Roylott, as he investigated recent events at the family home, Stoke Moran. Holmes comments on this in the final line:

 I am no doubt indirectly responsible for Dr. Grimesby Roylott's death.

It is very unusual for a Sherlock Holmes story to end so abruptly and on such a serious note. The reader is used to Sherlock solving crimes, not committing them, and to ending his investigations on a jubilant note, as the perpetrator is caught and Holmes explains his genius powers of investigation to an admiring Watson. Thus, "The Adventure of the Speckled Band" contrasts sharply with other stories and is, therefore, far more serious in tone.

In addition, the mood at the end of this story is reflective due to the moral nature of Holmes' role in Roylott's death. While Holmes does not feel any guilt regarding the man's death ("I cannot say that it is likely to weigh very heavily on my conscience"), this closing remark encourages reflection. Here, Doyle is inviting the reader to consider Holmes' role in the death: is Holmes right to be so dismissive of his involvement or should he better consider the moral consequences of his actions? Doyle leaves the reader to decide while Holmes prepares for his next case.