I really liked this, especially the ending, where the sepia illustrations took it back to the world of Katie's fics, and sort of made it back about the relationship we can't see (on screen, in canon pages), and the way she overlays the music of love and longing onto the familiar bodies to make them aching and hurting in a way we don't get to see, but we know exists.

Yes, exactly! I wanted to pull the viewer back to the idea of the books as the text source, so that the "book of love will let us in" line would have a broader application. That's what I think Katie does: she opens up the canon source for us, and gives us the love stories that we want, and that Conan Doyle could never, ever show explicitly in the text at the time that he was writing.

I really like what you do with the exchange of glances, too

Thank you! The heated exchange of glances is one of the main tools in my slash kit. :)