I've gotten most of the way through the deductions set piece. I'm at the required "Holmes explains the deductions to Watson" phase. Giles, who is familiar with the great man's methods, does not need the explanations, but is in a state of bemused awe as he watches the familiar process in person.
It's kind of a neat writing challenge: Imitate first-person Watson style, as seen in his journal. Which doesn't have to quite be the same as the published stories, but needs to be close. Through Watson's writing, show off Holmes, and Watson's attitude toward Holmes. Show Giles, and Giles' reactions to the famous men in the room with him, in terms that would be natural for Watson but give my clued-in modern readers more information than Watson himself gleans. And we can't help but learn all about Watson, so get that right too.
This is a standard first-person viewpoint writing problem, now that I think about it. Fun fun fun!
The Giles bits are easier, I think, because he has more information to start with. He's closer to the viewpoint of the reader. I can also make him more self-reflective than Watson might be. Or so I'm thinking right now.