The mood of "The Adventure of the Speckled Band" is suspenseful, tense, and apprehensive. The story constantly reminds the reader that Sherlock and Watson are in grave danger during their investigation, which leaves the reader in fear of what will happen next—and encourages them to keep reading in order to find out. The mood also becomes foreboding when Sherlock and Watson spend a long night waiting in darkness to unearth the truth of the crime. Watson exclaims:
How shall I ever forget that dreadful vigil? I could not hear a sound, not even the drawing of a breath, and yet I knew that my companion sat open-eyed, within a few feet of me, in the same state of nervous tension in which I was myself.
Watson's rhetorical question here ("How shall I ever forget...?") highlights the memorably perilous nature of the investigation and deepens the foreboding mood. His reference to his "state of nervous tension" amidst sheer darkness and silence enhances the reader's own apprehension of the unknown hazards of the manor, waiting to discover the truth of the crime. This tension culminates in the climactic death of Dr. Grimesby Roylott, when the mood transforms into horror at the grotesque nature of the crime.
