The last time we saw the character of Sid Baker in Slow Horses she was most decidedly dead. To paraphrase another British TV hit, Monty Python’s famous dead parrot sketch, Sid had ceased to be. She was an ex-spy. A bullet in the head will do that to you.
The bullet hit her early in season one, broadcast in 2022, when she was on a case with her Slough House partner River Cartwright (Jack Lowden). Was that some sexual tension we sensed between them? Why yes, it most definitely was, which made it all the more tragic when Sid got got. And so off Olivia Cooke went to make House of the Dragon, achieve global fame and look back on Slow Horses as the streaming TV mega-hit that got away.
Yet viewers of the second episode of season six of Apple’s British spy show were not mistaken: that very much was Sid Baker cropping up at the end, luring River to a safe house like the past four years had never happened. Readers of Mick Herron’s source novels knew this was coming, but Olivia Cooke did not, at least not at first: when she was cast in early 2021, Cooke assumed that Slow Horses would be a one and done.
“I was devastated because I really got invested with River and Sid, but I knew that I was always going to get shot in the head and disappear. Which is a funny thing to know,” she says.
“Disappear” is the key word there. Sid, it emerged, wasn’t dead, she had just been put in an induced coma. Towards the end of series one it was revealed that MI5 had no record of anyone called “Sidonie Baker” ever existing. In backstory, in Cooke’s mind at least, “there was an intense rehabilitation process where she had to learn to talk and walk again. She made a miraculous recovery!”
Further episodes of Slow Horses revealed that Sid had been a plant from MI5 boss Diana Taverner (Kristin Scott Thomas) to keep an eye on River.
“The years in the interim have been incredibly lonely for Sid, with a lack of autonomy as well,” says Cooke, “because she’s been in this holding pattern with Taverner, not really knowing when she’s going to be used, if she’s going to be used again, or why she’s being held in this certain location. Until she feels like someone is after her. And then the only person she can think of who she felt relatively safe with is River. That’s why she goes hunting him down.”
Between Sid 1.0 and 2.0 Slow Horses has galloped from strength to strength, even without one of its best characters. (In fairness, it seems to kill off a fan favourite almost every season). In the last three years the spy thriller has racked up 23 Emmy nominations, including three wins, and is regularly cited as one of the best shows on TV. Cooke, meanwhile, has had to watch and wait.
“There were various availability checks over the years and then I was also badgering my agent because I remained such a massive fan of the show,” she says. “The call came at the end of 2024 — ‘They want to shoot with you and here’s the story breakdown.’”
Sid reappears just as the slow horses – a group of washed-up MI5 agents sent to a backwater office to see out supposedly mothballed careers — find themselves being gunned down, one by one, by a pair of ruthless Russians (MyAnna Buring and Kyle Soller). Sid finds River before the Russians do, and together they head out on the run together.
“We did it within five weeks,” Cooke says. “All night shoots. It was just a delight. Adam [Randall, the show’s Emmy award-winning director] would have to tell me on many occasions, ‘Olivia! You’re being chased … stop looking like you’re enjoying it!’”
Cooke’s return was complicated by three things. First, writer Mick Herron had to resurrect Sid in his stories (which he duly did in the 2021 book Slough House). Second, the TV series had to catch up with Herron’s books – this sixth season is based on his sixth and seventh books, Joe Country and Slough House). And finally, Cooke had to find time to film it – a lead role in HBO’s swords and sorcery behemoth House of the Dragon as Queen Alicent Hightower meant she was already a little busy.
“I remember seeing Jack [Lowden] or Saskia [Reeves, who plays Catherine Standish] over the years, and they’d be like, ‘When are you coming back? You know, you are coming back, right … you’re in the books! We’re waiting for you – don’t let dragons get in the way! Don’t get too big for us!’”
That was never going to happen. Cooke is about as down to earth a screen star as you could wish to meet (she even asks for permission to take her shoes off and put her feet on her own sofa during our Zoom call).
“I just said, ‘Are you joking me? I’m absolutely desperate to come back.’ I’ve been what the kids would call ‘bread crumbed’ for the past four years [giving someone sporadic, low-effort attention to keep them interested without ever intending to commit] – while also watching as a fan and being green with envy that everyone’s having such a good time.”
Sid Baker is a fan favourite not least because she was, and now is again, a small shaft of light in Slough House’s roster of embittered doom-mongers. Cooke likes the role for the same reason.
“I tend to play very morally complicated and depressed characters. Whereas there is an effervescence with Sid that I really love,” she says. “That’s such a nice quality to sort of shine through the prism of myself – not to be all Daniel Day-Lewis, but you are affected by what you play. It does get to you after a while and so playing Sid and having this really fun, sparkly relationship with River is just a joy. Let’s just say that the veil is very thin – I don’t think she’s too far away from me.”
As that suggests, Sid works best as one half of a double-act. Some of season six’s best moments are in Sid/River two-handers, both of them ripping it out of the other one, no matter how close peril is to hand.
“Jack [Lowden] and I have always had that vibe where we do just take the piss out of each other,” Cooke says, laughing. “That has been set from day one. Initially, the scripts enhanced that dynamic. Now it has evolved into … mild bullying.”
Who does most of the bullying? “Maybe I bully him a bit more, but it’s also that British humour that I think the rest of the world loves so much. Everything mean and nasty is said with a wink-wink, nudge-nudge and we sort of get away with it. We can’t say what we mean, and we don’t really give eye contact, but being rude about each other is our way of showing love.”