I was listening to an explanation of standard movie plotting versus television plotting last night and had an odd realization about our friend Mr. Sherlock Holmes: He can never change.
When Conan Doyle first created the detective, he was doing something ground-breaking: Putting together a series of stand-alone short stories that featured ongoing characters. Basically, he was inventing the TV series before television came around. And if you look at the way a typical American TV show is plotted, you can see it applies to his work as well.
In any good stand-alone fiction, be it a movie or a novel, the important characters follow a structure akin to Campbell's "Hero's journey" -- the character leaves their familiar world behind, goes through an adventure, and comes back changed forever. Whether it's as simple as finding a courage they never had or getting a romantic partner, or as complicated as a transformation into a master of some area of skill they had never even heard of before their adventure began, the hero and their world changes.
The closest thing we find to this in the Holmes Canon is Watson's transformation from recovering veteran to detective's companion in A Study in Scarlet. But once that change is done? Suddenly the Canon becomes all television series writing.
Because standard TV writing isn't about change . . . it's about preserving the status quo. Movies are taking a turn that way as studios try to produce endless sequels and become just giant TV series, but the TV story arc is a different one: The hero is presented with something that messes up the status quo of their TV world, they spend an episode fixing it, and the status quo is saved at the end of the show. Come back next week for more Xxxx Xxxxxxxxx!
If there was ever any doubt that BBC Sherlock was television and not movie writing, the last episode of season four pounds that difference home with the near-magical restoration of 221B Baker Street after it is blown to bits. Even Sherlock Holmes's huge life-defining revelation isn't there to change who he is but to cement who he is by giving him an origin that explains him.
Sherlock Holmes cannot change in the mainstream, because he's a serial character. He and Watson cannot find love and live happily ever after. He can't be a drug addict, work through his addiction and recover. He cannot be anything but Sherlock Holmes, because at the end of the day, he has to return to being Sherlock Holmes. And he didn't start as an addict or in love with Watson. Those are left for the black market of fan fiction, where all the character development we normally want from a person gets to play out. (And I would argue that even The Seven-Per-Cent Solution is pure fan fiction, creating a Holmes so based in delusion he could not survive ongoing stories.)
The original stories feature arc where character's lives changed forever, but those were always the clients. Even the most dramatic moments in Holmes's life -- Reichenbach, retirement, becoming a spy -- didn't change him. They were just attempts by his creator to have a final episode and be done. The short stories are always more of a tale about the clients with Watson narrating and Holmes being their wise guide through the dramatic change in their life.
We've seen an alternate version of Holmes support a series: CBS's Elementary or the cartoon Sherlock Holmes in the 22nd Century, but those both start with a very different Sherlock Holmes who remains in a very different status quo throughout his series. Someday, I'm sure, we will get a series where Holmes and Watson are in love from the start and solve cases while working through their relationship.
Likewise, we'll always get stand-alone movies where Holmes changes for just one story -- like Without A Clue, Young Sherlock Holmes, or Mr. Holmes -- but again those are alternate Holmeses created for the telling of that one tale. In order to be Sherlock Holmes, in order to solve mysteries and bring rational explanations to a world of strange events, our favorite detective must not only champion scientific and rational thought, but a certain basic status quo of reality itself.
Can Sherlock Holmes change? I really have to wonder.