Mr. Moore interjects a young woman named Sarah into the story, mostly because he has to. Sarah says that she’s a reporter covering the convention, that Harold will make a nice hook for her article, and that she must thus join him in globe-trotting in order to witness his adventures. This makes her the least credible character in a book that crosscuts between Harold in the present and Arthur — as Conan Doyle is called here — in 1900 and gives Arthur a sidekick too. Arthur is accompanied by his friend Bram, an aspiring writer who is as obscure as Arthur is famous, since nobody cares about Stoker’s Transylvanian “Count What’s-His-Name.” Feel free to enjoy the fact that there will be a Count Chocula more than 100 years later.

The passage of time between Arthur’s era and Harold’s actually lends some gravitas to the fun and games “The Sherlockian” provides. Harold thinks wistfully back to the relative simplicity of Conan Doyle’s time (even though Mr. Moore’s historical research makes it clear that Conan Doyle faced plenty of real problems). “It’s funny,” Harold says, once the plot takes him to England. “I’m so much more familiar with Britain a hundred years ago than Britain today.”

And every time the book’s 21st-century chapters refer to new technology, they contrast sharply with late Victorian glamor. “The old centuries had, and have, powers of their own,” writes one Sherlockian, “which mere modernity cannot kill.” Mr. Moore sustains this theme so faithfully that his book’s last chapter, about the arrival of so-called progress on Baker Street, is its most affecting one.

So “The Sherlockian” manages to make a journey from the ridiculous (Harold White, instant detective?) to the sublime. And it is anchored by Mr. Moore’s self-evident love of the rules that shape good mystery fiction and the promises on which it must deliver. As the book’s characters say outright, all the relevant details must be woven into the story. There can’t be too many needless ones. Progress must be logical. The author must understand, as Arthur demonstrates during the course of this novel, that “the requisite pedantry of detective work” does have its obsessive-compulsive rewards.

And the author must make a promise to his readers. It is a vow that is made explicitly by Arthur during “The Sherlockian” but is honored in this book by Mr. Moore too. “I am going to take care of you,” Arthur avers. “I know it seems impossible now, but it will all work out. You cannot see where I’m going, but I can, and it will delight you in the end.”