Is the plot for this Sherlock series 4 episode already online?

While we know that Sherlock episodes can often deviate wildly from the stories that inspired them, the Lying Detective looks like he could have quite a bit in common with his Dying counterpart. Back in July we learned via San Diego Comic-Con that the story would be linked in some way to the word 'Smith', and following that Cultbox dug up a CV that reveals guest-star Toby Jones is playing none other than Culverton Smith, the character who in the original story attempts to murder Holmes with poison.

What exactly The Six Thatchers might entail, though, is not immediately clear. When the word 'Thatcher' was revealed at Comic-Con, topics of speculation ranged from the former PM (of course) to theories about traditional roofing practitioners and a certain brand of Somerset cider. And when the full title was unveiled, my initial instinct was that it was likely to be more about the play on words and less about what will actually be going on in the episode

But then I remembered something.

The Six Thatchers actually refers to a case that Sherlock and John have already solved.

Look, it’s all here in an entry in John’s blog, dated 19th December.

In case you weren’t aware of it, this is the official BBC blog associated with the series, which outlines stories we’ve seen on screen, others that have only been mentioned in passing – and some we haven’t yet heard of…

And based on John’s description, The Six Thatchers sounds very similar indeed to The Six Napoleans...

**possible spoilers follow**

The Conan Doyle adventure concerns a mysterious series of burglaries that each culminate in the theft and destruction of an identical plaster bust of Napolean – and once in murder. It eventually transpires that the thief had hidden a valuable black pearl inside one of them and was attempting to track it down again.

In the case described in John’s blog, the Napoleans become busts of Margaret Thatcher, and the item hidden inside one of them is the penknife used in the murder but the basic premise is the same. So is the culprit – in both, he's an Italian named Beppo.

So, could this really be the plot to The Six Thatchers we’re going to see on screen?

Well, John’s story is set at Christmas (it features a vignette in which Sherlock is escorted away by police after demanding in front of a shocked group of children and their parents that a department store Santa bring him “a nice juicy murder for Christmas”, something you can very much imagine him doing in the show itself) and the first episode of a new series of Sherlock traditionally arrives on 1st January, so a seasonal themed story is not at all out of the question (and it wouldn’t be the first).

The fact that it has the same title as the blog seems unlikely to be a coincidence either – it’s no surprise that such a popular story as the Six Napoleans is one that Sherlock co-creators Mark Gatiss and Steven Moffat have also chosen to adapt but the idea that they and Joseph Lidster (who – sorry to shatter your illusions – actually writes John's blog) would independently choose to substitute Napoleans for Thatchers seems far-fetched to say the least.

So could Gatiss and Moffat have suggested the idea to Lidster then forgotten they'd done so when they came to write the new series? It's possible, but kind of hard to believe given how rigorous they are and how well they seem to know their own work.

As always with this mischievous pair, the other option is that they suggested the blog idea, then a couple of years later thought it would be amusing to use the same title to see if anyone picked up on it.

Either way, there's a good chance it won't be the same plot at all. You'd think Lidster's version is likely to have been fleshed out by him, probably based on the original Sherlock Holmes story. Gatiss and Moffat probably won't stick so closely to the original (they rarely do) but even if they do they're unlikely to come up with exactly the same ideas.

If the two really are different, though, that means the BBC Sherlock canon – which John's official blog must be a part of – will now have two different cases with the same name, and for fanboys like Gatiss and Moffat, surely that can't sit comfortably either.

The further you dig into it, the harder it is to fathom exactly what's going on here – but with months to go until series four of Sherlock, another mystery could be exactly what fans need to tide them over...