As Holmes and Watson were not yet in the public domain at time of publication, Harry Turtledove obfuscates their identities. He also makes the Watson analog a passively racist xenophobe, whereas the original character was quite enlightened and tolerant in that regard. The title is a reference to two of Doyle's Holmes stories: "A Study in Scarlet" and "The Adventure of the Speckled Band."
The English detective Athelstan Helms, and his associate and biographer Doctor James Walton, travel to Atlantis in the 1880s to help authorities investigate a series of murders. The victims were all critics of the House of Universal Devotion, a homegrown religion. Naturally, the authorities (and Walton) are convinced the House is responsible, but Helms isn't so certain.