For several seasons of Slow Horses, Sid Baker has existed almost like a ghost. Shot in the head during the first season and subsequently presumed dead, the capable MI5 agent disappeared from Slough House, leaving River Cartwright – and audiences – without any real sense of closure. But Sid wasn’t dead. She was simply living a life that had become increasingly small, isolated and, crucially, controlled by someone else.
Now, as Slow Horses returns for its sixth season, so too does Olivia Cooke, stepping back into a character she hasn’t played in years and finding a woman profoundly altered by everything that happened off-screen. Sid’s return isn’t simply about rejoining Slough House; it’s about reclaiming an identity, an autonomy and a sense of purpose that were effectively taken from her.
Speaking with our Peter Gray out of Toronto ahead of the sixth season premiere, Cooke reflected on returning to Sid after such a significant absence, the anger beneath her character’s re-emergence, and what years without autonomy have done to her sense of self.
Sid has had this extraordinary experience where, in a sense, she’s had to live with her own death – everyone she knew believed she was gone, and the world effectively continued without her. When you were finding her again, did you think about what that does to someone’s relationship with their own identity? Is she still Sid Baker when Sid Baker technically stopped existing?
I think there are obviously large remnants of her in there, but I think she has lost herself along the way. She’s lived an incredibly lonely existence. I don’t think Diana Taverner (Kristin Scott Thomas’s character) has told her barely any truth about what her situation is, and I think she’s just been in a holding pattern until she feels like, “Oh no, I think my life is in danger again. I know what that feels like, to almost lose it, and I don’t feel safe.”
Who’s the one person in recent memory that I did feel safe with? That’s River (Jack Lowden’s character). And so, hence, she goes looking for him. But I do think she’s lived a very solitary life for a few years, and it’s not an easy way back into the dynamic they had in the first season. It’s wrought with tension and confusion, and it just feels like there’s a lot of stuff in the way.
Mentioning River, I feel like there’s not really closure there, and that relationship almost gets frozen at a point where something might have happened between them. When they see each other again, did you and Jack think about the things that have been allowed to grow in that silence?
I think, for Sid, she’s sort of mythologized River in a way. They had such a brief time together, but it was so rich and sparkly. And, you know, when you feel like that for someone, it does feel like you’re at the pinnacle of living because everything sort of gets going in your body. You feel really alive.
And so I do think she’s sort of made this legend of their time together. I think that’s why it’s so confusing when they’re confronted with each other again, because it’s like wading through tar trying to get to that place again. And, you know, I think she has been extremely lonely. I don’t think she’s had much real contact with other people, and this has been the last sort of semblance of fledgling romance for her.
Sid is one of the more competent people in the house. Lamb (Gary Oldman’s character) called her “the only good one” at one point, but then her career and identity is taken away from her. Do you feel there was a lot of anger in that return? Not necessarily explosive, but the anger of having had her life decided for her?
Yeah, well, she was planted in Slough House. Diana Taverner had planted her there to keep tabs on these people, and specifically on River. So she is the most confident. She has no business being at Slough House as one of the rejects – no offense (laughs).
I think when you’re so good at something and you can no longer do it, for whatever reason, it feels like a limb has been torn off. A very existential feeling comes over you. You start asking a lot of questions, like, “What is my purpose? What’s the point? Who am I now? Do I just exist in this form where I’m collateral, or a spare part to be used somewhere down the line?”
There’s no information and there’s no autonomy. So, yeah, I think there’s a lot of anger that comes from having so many questions, being kept in the dark, and knowing how brilliant her mind is and how adept she is, but not being able to fucking use it.
Yeah, absolutely. A few years ago, something really terrible happened, and I started to question my own abilities in terms of writing, interviewing, and the things I love to do. I had to go back to that and remind myself, “You’re actually good at this.”
I look at TV, movies and shows as this safe space. This is what I know, and this is what I know I’m good at. So I really understand that feeling of having something taken away from you and suddenly asking, “Who am I?” You have to find your way back to that part of yourself and realise, “No, I’m actually really, really good at this.”
I think that’s why people relate to Slow Horses so much, because these are people who have done one thing wrong and then they’re put out to pasture. They’re basically filing cabinets for the rest of their lives.
Especially with River, his main goal is to get back to the Park and prove to people that he is competent and that he is good at what he does. But they’re just not given that chance. And, you know, everyone loves an underdog trying to fight the system.
I feel like actors usually get to build a character through continuity, and you had this enormous interruption. Did that distance actually give you something useful? Because Sid herself has lived an entire life that neither we nor the other characters witnessed. Did you have conversations about what she had been doing during all that time away?
Yeah, we did. I think she was at a rehabilitation facility that a lot of ex-spies who have been injured doing field ops go to. It’s a very secretive place where you get rehabilitated. Then I think she was put in a secure location somewhere in Cumbria, out in the countryside, where she’s essentially been told, “Wait until we call upon you.”
That does a lot when you don’t have any autonomy. She’s basically been a prisoner, and her life has gotten so, so small.
I think it was really helpful for me coming back to Sid because I’ve also had so much time away. In the interim, we’ve all had things happen in our lives. We’ve kept in contact, or tried to keep in contact over the years, but there are huge swathes of time where we don’t see each other.
So I entered the season playing Sid, but also as a different person myself. I think some of that has seeped in. I can’t help but have that be the case, because neither Sid nor I have been cryogenically frozen (laughs).
There’s an unusual kind of power in being presumed dead. Sid has had all these years where nobody from her old life could ask anything of her. Does coming back almost mean surrendering a certain sense of freedom as well?
Yeah, a little bit, because I think Sid has seen death. She’s seen rock bottom. She’s seen how bad it can get. Going from someone hunting her down to going to River for help – it’s better than the alternative, isn’t it?
And there is a freedom in this. I think what was really nice to play was that there’s a giddiness as well. Even though she’s a woman in her 30s, there’s a childlikeness to seeing him again and having this moment frozen in time with River, because she’s just been so starved of that connection for so long.
The sixth season of Slow Horses will premiere on September 16th, 2026, with the first episode, followed by one episode weekly until 21 October.
