OK, we all know that fans can get a bit silly. Think of Tolkien enthusiasts practicing their spoken Elvish at conferences, or Anne Shirley groupies traveling to PEI in order to get married at Green Gables.

Add Sherlockians to this crew, the devoted fans of that paragon of the uber-intellectual detective, fans who can match each other, quote-for-quote, from the Holmes archives. It should surprise no one how many of this particular group behave as though Sherlock were a real person and not just the clever creation of a failed medical doctor.

Don’t get me wrong. I may not be one of these fans, but I still admire most of what Sherlock stands for — intellect, reasoned thought, expertise (no matter how arcane). Conan Doyle’s stories have stayed with us because we love watching the tangled strands of a mystery being pulled apart, to reveal the solution. Whether by Miss Marple, Hamish Macbeth, Jane Tennison, or Sherlock himself — the challenge is to see how much we can get ahead of the story. Has the author laid enough clues for us to outguess the detective? or so few that we can’t even follow the solution?

But I find myself getting away from the point here, which is Moore’s book, about Sherlockians and Conan Doyle himself. Moore gives us two murder mysteries that parallel each other, one in 1900 and the other in 2010. Conan Doyle uses Sherlockian logic to solve the Victorian mystery, and his devoted fan, Harold White, does the same in the more modern era. Is it possible to use intellect to solve horrifying murders? or is Conan Doyle’s creation a logical impossibility?

Moore’s plot works something like an echo chamber, with themes, events and devices caroming back and forth across the 110 years that divide the two main characters.

In 2010, at a convention of the Baker Street Irregulars, a man about to announce the discovery of Conan Doyle’s missing diary (covering October to December of 1900) is found strangled in his hotel room. The game’s afoot, and Harold is happy to prove his intellectual mettle, with an unflappable female freelance writer acting as his Watson.

Back in 1900, a failed letter bomb puts Conan Doyle on the trail of a serial killer, with the unflappable theater impresario Bram Stoker (yes, him) as his sidekick.

Now, back to my earlier tangent. This isn’t just a book about solving two murder mysteries. It’s also about Conan Doyle’s decisions, first to kill Sherlock at Reichenbach Falls, and then subsequently to resuscitate him. It’s about mystery plots and the function of the sidekick (if Watson had been as smart as Holmes, we’d have known the solution immediately and missed the pleasure of piecing together the clues that Holmes reveals to his buddy). At its most basic, this book is a test of Holmes’ methods. Conan Doyle and Harold White believe so firmly in deductive reasoning that, contrary to reason, they assume they can find the murderers where experts have failed. If they don’t, does that mean that Sherlock is just a ridiculous fantasy?

Well, something else that Moore explains through his characters is why murder mysteries must end with the exposure of the villain. Unlike real life, there can be no other ending. So we can trust that Moore himself won’t leave us hanging.