Because the true canon of the Sherlock Holmes mysteries ceased around 84 years ago, and it was limited to a mere 60 tales plus apocrypha, even fans like me who feel no particular need to seek out fanfiction for other properties have a ravenous appetite for even terrible new stories. Mere faithful film adaptations aren't enough, we crave new tales. We want those stories Watson hinted at. We long for the stories that were too shocking and too entangled with the news of the day to publish. We seek out the confrontation with Jack the Ripper. We need the build-up to The Final Problem. We demand The Giant Rat of Sumatra and the other stories for which the world was not yet prepared.
Fortunately, there is no shortage of writers willing to give us new mysteries. Though the quality varies from time to time. (Do not read any take on The Giant Rat of Sumatra. It is no fault of the ambitious writer who tackles that tantalizing title that it is too much to live up to, but it is simply a fact that no rational explanation could live up to it.)
I've read some truly awful Sherlock Holmes fanfic in my day. And I don't mean awful because we found it on some poor young person's unprotected tumblr, I don't mean the sort of awful that was dashed off in an hour in response to a kinkmeme. I mean stuff people actually got professionals to publish and stock in bookstores.
But I've read some pretty good stuff. I've read some stuff that is pretty good despite falling to the perilous tropes of fanfiction, where the writer's style is aped awkwrdly and there is fanservice thrown in to the detriment of the story momentum.
And I've read some pretty great stuff too, some great stuff that no one has been willing to publish even. (Why is Marcia Wilson's You Buy Bones self-published when the first half is better than most of the stuff put out in the last 84 years?)
So even when I saw that little sticker saying that ACD's descendants have put their stamp of approval on the story, I still consider it fanfiction and I donn't mean that to diminish it. It was professional published by an bestselling writer, so I expected one of the better works I'd seen but I didn't expect it to succeed in capturing the style of the original sixty stories. But to that end, the House of Silk may be one of the finest pieces of fanfiction ever written.
This is probably due to his conscientious avoidance of the habits that annoy me the most about contemporary Sherlock Holmes writers. The mysteries are completely original plots that do not erase any of the canon stories. (Contradictions are okay, ACD did that all the time and we just blamed it on Watson being a bad notetaker, but I can think of a number of works that exist on the premise that entire stories were inventions of Dr. Watson.) All of the dialogue is new, no seeing Sherlock reuse his old phrasing in order to make him sound like himself, but it effectively captures the voice of the original writer. He alludes to other stories, but in a way that seems natural to Watson's train of thought. The characters are true to the original stories, while fitting the nicely into the trends of modern fiction. Horowitz's Watson is familiar and strong enough to carry the plot when Sherlock is out of sight. His female characters live up to modern expectations of character without being unrealistically enlightened for the era. New characters fit nicely into the traditional roles allotted for new characters: clients, villains, and victims, and he doesn't try to introduce a new detective or partner to tag alongside the main attraction. The appearances of fan-favorites like Inspector Lestrade and Mycroft Holmes aren't just a favor for the fans, their presence is logical and important to moving the plot along.
That's not to say there aren't continuity errors, contradictions, odd reasonings and other little problems. Thing is, all the little errors in this book are along the same lines of the sorts of errors ACD made back in the day. The real triumph of this work is that he manages to capture the voice so well. I suspect there was meticulous editing and rewriting to make the style match without just copying it. When you read this, you are reading something written in Dr. Watson's voice.
And he does that without sacrificing any of the other necessary elements in the book, the characterization and plotting are all up to par.
I only have one word of warning at the risk of spoilers, and that is that when the promotional materials state that this is a story too shocking to have published a hundred years ago, they aren't exaggerating. The book captures the Watson voice so well I just blew that off because that character has a very different idea of lurid that I do. The events depicted could easily have happened in the 1890s but would never have been published. I recommend this book, but with a trigger warning for sexual assault. True to the Watson voice, though, Horowitz doesn't linger over the details. It's referenced, not explicit, and not against a major character.
The House of Silk by Anthony Horowitz