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. Turtledove suggests in Other Places that the title is a reference to two of Doyle's Holmes stories: "A Study in Scarlet" and "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.