Author's summary: “Favourite AU? John, what does that even mean?”
“Just go with it, Sherlock. And don’t ruffle your hair.”
“And why is there still no signal on my mobile?”
Reccer's comments: For those who don't want any information about the Special, I am putting this behind a cut: [Spoiler (click to open)]The costumes and poses of Sherlock and John are inspired by a manip of photos taken during the most recent Setlock. Both men are wearing costumes seen in Setlock images, which means they are wearing clothing that places them in the 1890s (the writers have recently emphasized that the year the Special is set in, 1895, is quite important). Bluebell here is playing with the AU nature of the Special (Late Victorian AU of a show that is a 21st-century AU of stories set in the Late Victorian and Edwardian periods), implying that the boys are 21st-century men in costume (for a case? John has a special kink?). John is certainly having fun (and is looking dashing)! In case anyone is confused, I'll add that although we know most or all of it is set in the past, no one knows yet how the Special will be framed.
I had been a bit worried that the costuming for the Special might be horribly inauthentic, because my cranky Inner (and Outer) Historian finds it hard to watch film and TV set in the past with clothing that little resembles the clothing people actually wore. Thankfully, it looks like they wanted a more authentic look! John's wearing a ditto suit (all three pieces use the same fabric, the jacket is a sack coat), whereas most of Sherlock's green suit is hidden behind the famous greatcoat and deerstalker hat. The rendering of both men's faces is wonderful: a study in contrasts (confusion and maybe the start of a sulk vs. John enjoying it all)