Three Blind Bankers
I started to write a response to this thread, and it became too long, so here it is on its own.
The bank in The Blind Banker is indeed metafictionally important—as @thewatsonbeekeepers says, John acts as Sherlock’s “agent” in this episode, collecting money for Sherlock’s services. It’s an old custom of the Sherlockian societies to refer to Arthur Conan Doyle as Sherlock Holmes’s “literary agent”, rather than the writer of the stories (because, as we all know, John Watson actually wrote them).
Having John Watson feeling cash-poor and turning to Sherlock Holmes for help, then insisting he be paid, his physical expression of relief when he takes the cheque… all of this is very reminiscent of Arthur Conan Doyle, who was desperate for cash in his early years. The shadow of that desperation never left him, even after he started making big money from Sherlock Holmes. And the common perception is that Doyle would also turn to Sherlock Holmes only when he needed money.
Regarding the idea that the bank represents “the estate”, it’s important to remember that there is not a single Doyle estate, but two: the Sir Arthur Conan Doyle Literary Estate and the Conan Doyle Estate Ltd. (which is the one linked in the previous discussion). Both have (or have had) family ties to Arthur Conan Doyle, both have separate legitimate claims to specific parts of Doyle’s legacy, and both have brought copyright lawsuits under different circumstances.
The posts that used to circulate on tumblr about Andrea Plunkett and her nuisance lawsuits against various film adapters were about the Literary Estate. The nuisance lawsuit against the Enola Holmes adaptation was brought by the Conan Doyle Estate Lid. The Conan Doyle Estate Ltd. is also the group that is closely affiliated with a number of highly esteemed Sherlockians, including those who are slowly releasing previously unpublished works by Doyle, like the whaling diary Dangerous Work and A Life in Letters. This group is trying to shut down Enola Holmes. They also have a stake in presenting Doyle and Sherlock Holmes in a specific light, and they control a lot of information about both. So, paraphrasing from the previous discussion, “Have they ever read the Canon?” Oh yeah. They’ve read it, published it, interpreted it, made careers and reputations on it. But they don’t see it the way we do.
To return to Sebastian Wilkes, I’m not convinced that he represents either or both of the estates, although perhaps I am wrong. The thing is, Sebastian’s relationship to Sherlock in TBB echoes John’s: this case is costing him, in terms of money and potential embarrassment. His response is to turn to Sherlock Holmes… “How’re things, buddy?” he says. His tone is ingratiating… Can you help me out here? Could you see your way? Would you sort this for me? Could you be discreet? These are the same sentiments, from both John and Sebastian, in the same episode.
The difference is all in the attitude. Hard to imagine John saying here, “We all hated him” even if he does laugh at Sebastian’s joke. Sebastian looks down his nose at Sherlock, even as he save’s Sebastian’s livelihood… which is exactly how Doyle acted toward Sherlock Holmes within his lifetime. Doyle insisted repeatedly that Sherlock Holmes kept him from writing better things, that he only came back to the Holmes stories for money. So, there’s a lot of conflation here, I think, between Doyle, Sebastian Wilkes, and John Watson. It gives us a little glimpse at John’s imperfection and at his subterfuge. For a number of reasons, I think it is unlikely that Doyle really hated Sherlock Holmes, but publicly, he insisted that he did.
So, I think Sebastian Wilkes is specifically a mirror for both Doyle and John (or simply for John via Doyle) in this episode. The bank itself mirrors Doyle’s legacy, as @raggedyblue suggested. And perhaps the fact that it is a bank means that it represents what people stand to gain from it. That is the business of the estates, and also of everyone who produces content related to Sherlock Holmes, including filmmakers, publishers, pastiche writers, old-school Sherlockians… and even us.
However, the name of the bank, Shad Sanderson, suggests to me that Mofftiss aren’t aiming at so broad an interpretation. Etymologically, Sanderson is the same name as Anderson, who we recognize as an obvious John mirror. And I strongly suspect that Shad is taken from Shad Thames, an old London street near Tower Bridge; the name of this street is a corruption of “St John’s”.
So, this is John’s bank—of stories, really—presided over by a portrait of Doyle, and Sherlock Holmes enters at the invitation of a sneering John mirror to solve a case there. There is much in this episode that we couldn’t have recognized when we first saw it in S1, but that becomes clearer in hindsight.