A lot of story was crammed into the final minutes of Sherlock series 4. The musical montage took us from the detective's violin duet with his disturbed sister Eurus in her island prison, back to Baker Street and a whirlwind of previously unseen cases (including that dead Viking), before Sherlock and John emerged dynamically from "Rathbone Place", off for more adventures that we may or may not get to see.

With the cast and writers unsure at that stage whether they would ever make more Sherlock, those last moments were specifically designed to leave us at a point which could work as either an ending or a new beginning – and they did so perfectly without the need for words.

It's interesting to learn, then, that dialogue had originally been written to come after the montage and was only dispensed with when writers Mark Gatiss and Steven Moffat realised that the orchestra could do the job on its own.

Speaking at a session about the music of Sherlock at the BFI & Radio Times Television Festival, Gatiss described how the score by composers David Arnold and Michael Price had been integral to those final scenes.  

"The only way [Sherlock and Eurus] can communicate now is through music," said Gatiss. "That was the idea – and that from this tentative start... everything starts to become more optimistic and we kick into the montage.

"But we did actually have some dialogue that was going to follow it and we realised as soon it was all coming together that it was incredibly eloquent and it told you everything you needed to know... the music speaks for everything."

But what could that dialogue have been? Was it between Sherlock and John? Given that Rathbone Place is a reference to an earlier incarnation of Sherlock Holmes, could it have echoed that and given us some kind of classic Holmes reference? And would it have told us any more about what happens next to our partners in crime solving?

Sadly, Gatiss is staying tight-lipped about that but he did point out that as the duo leap from Rathbone Place into their futures "we don't know if they made that last step".

Maybe those final words were simply "Aaaarrgh!"