Olivia Cooke is back in Slow Horses, but Sid Baker cannot simply walk back into her old life. The MI5 agent survived the first season’s shooting and disappeared while the people around her believed she was dead. Season 6 brings Sid into view again, carrying years of loneliness and anger.
The new season premiered on Apple TV September 16. In a fresh interview, Cooke describes a character who has lost the work that once made her feel capable, spent years waiting for answers and finally seeks out the one person she remembers feeling safe with: River Cartwright.
Sid has to find out who she is now
Cooke says Sid was kept in a small, solitary life after her injury. She believes Diana Taverner did not tell Sid enough about the situation she was in. For an agent who trusted her own mind and skills, being left with no clear job or freedom to act is not a peaceful retirement.
The actress makes the anger understandable without pretending Sid has all the answers. Sid was good at what she did. Losing that purpose, and feeling like somebody else could decide when to use her again, has changed the way she sees herself. Her return is not a quick heroic entrance followed by business as usual.
Seeing River again is complicated
Sid goes looking for River, played by Jack Lowden. Cooke says she has held onto the memory of their brief time together, but the years apart did not freeze River in place. When they meet again, both have more to work through than an old spark.
That gives the reunion an emotional hook even for viewers who remember Sid mostly as a startling absence from the early seasons. Cooke is clear that the relationship carries tension and confusion. She is talking about how Sid feels going back, not promising a romance or revealing where the new season will leave them.
What else is happening in Season 6?
Apple says Jackson Lamb’s team is on the run as Diana Taverner pulls them into a dangerous game of retaliation and revenge. Gary Oldman returns as Lamb, alongside Kristin Scott Thomas as Taverner, Lowden as River and the wider Slough House ensemble. Cooke reprises Sid rather than joining as a new character.
The season has six episodes. Apple released the first on September 16 and plans one per week through October 21. The show adapts material from Mick Herron’s Joe Country and Slough House novels, but Cooke’s interview is about the person Sid has become after the time viewers did not see.
For the series background and season details, see our Slow Horses title page.
Quick answers
Who does Olivia Cooke play?
She plays Sidonie “Sid” Baker, the MI5 agent presumed dead after the first season.
When is Season 6 on Apple TV?
The first episode premiered September 16, 2026, with new episodes scheduled weekly through October 21.
