- They solve crime … IN SPACE. Maybe a Trek AU? Where Sherlock consults with Starfleet but isn’t a member, Joan used to be in the medical corps but now does not, and Moriarty is an interstellar criminal. Admiral Gregson! Bell is the captain of a ship that Sherlock and Joan are crimesolving passengers on! (Or maybe some kind of Firefly AU where Sherlock thinks his girlfriend Irene is being experimented on in a facility but actually she’s running it? And then things go much as they do in canon only In Space.)
- A fantasy AU of some sort, purely for the inevitable scene where Joan, just sitting up in bed, hears a loud, loud noise on the roof of the brownstone and closes her eyes because she already knows what happened, and what happened is that Sherlock adopted a dragon. She looks tragically at Clyde, who is a turtle in all universes, and gets up to call Elf Ms. Hudson to ask whether dragons need a particular kind of charcoal or will barbeque charcoal do.
- I want to say some kind of Marvelverse crossover, I think. Maybe Joan and Sam know each other? Maybe a Daredevil crossover! They both work with the law, and Daredevil is my favorite canon I haven’t consumed. But Joan + Sherlock + superheroes seems like an awesome idea. And then we could have superpowered Moriarty.
- Because I am too, too fond of the brownstone menagerie, the one where Sherlock is the grouchy zookeeper who knows every last thing about every last animal in his zoo and Joan is the new consulting veterinarian to the zoo (“I DON’T NEED YOU, WATSON, I MAY NOT HAVE A VETERINARY DEGREE BUT I AM PERFECTLY CAPABLE OF DIAGNOSING A PENGUIN”), and someone, I don’t know, steals a tiger or something? And they solve that crime.
- AU where they are an indie band? The Consulting Detectives! I don’t know, I am just tickled by the very thought of this.
The zookeeper AU and the fantasy AU are making me wish I knew how to art, the images I get are far too fun.