There was someone else in Eurus's prison cell apart from Sherlock star Sian Brooke...

Sherlock's series four finale was full of surprises – the non-existent glass wall, the endless and seemingly random murders, the true story of Redbeard – and just when you thought you could relax, here’s another one. Well, sort of...

Production designer Arwel Wyn Jones has revealed that there was actually someone else in Eurus’s Sherrinford prison cell apart from Sian Brooke, the actress playing Sherlock’s sister… did you spot them?

It turns out that in some scenes where her back was to the camera, it wasn’t Brooke after all – it was actually the violinist Eos (sounds a bit like Eurus) Counsell.

https://twitter.com/arwelwjones/status/821155641402265600

Looking back on it, she was playing to an almost inconceivably professional standard. It might have been a bit of a stretch to ask Brooke to do that after she already had to audition for three roles...