Sherlock Season 4: Sian Brooke on Keeping Her Role Secret

Warning: contains spoilers for Sherlock The Lying Detective

If you’ve seen "The Lying Detective"—and you’d better have if you’re reading this and don’t want anything spoiled for you—then you know who Sian Brooke plays in Sherlock Season 4: Sherlock and Mycroft’s secret sister Eurus (official spelling tbc).

To keep that under wraps, even Brooke didn’t know what she was auditioning for at first. As she told the audience at a BFI preview screening of the series four finale, she assumed it was just a bit part. “I just thought it’s a little part in Sherlock, it’s lovely”. When the show’s creators brought her back to audition for the multiple ‘bit parts’ that make up her character “I just thought they couldn’t make their minds up! When they actually revealed what it was, I was like, what? What? WHAT?”

Brooke was, of course, allowed to tell no-one. “They said you can’t tell anybody, which means you can’t tell anybody. Well, I had to tell my husband…” At which point Moffat and Gatiss interrupted with “We said nobody!” to a round of laughter.

“I had to tell my husband and my mum and dad because they had to look after my kids when I was going to Cardiff,” Brooke continued. To explain the regular trips to Wales to friends though, she was forced to lie. “Everyone else was like ‘where are you disappearing to? What are you filming?’  and I said ‘I’m just filming a new crime drama’ ‘Who’s it for?’ ‘BBC’ ‘Who’s in it?’ ‘Everybody’s new, you won’t know anyone, they’re all new faces…' I am so fed up of telling lies. I’m so relieved that it’s out.”

It must have felt satisfying to hoodwink the public though?

“That was great because the main objective, reading it, was to be able to hide in plain sight so I think there’s a lot of people to thank in the make-up department and costume department and the way it’s so cleverly edited.”

Sherlock season 4 finale "The Final Problem" airs on Sunday the 15^th of January on BBC One and PBS at 9pm.