Slow Horses is back with a bang, and the first episode of Season 6 wastes no time making things personal for Jackson Lamb and his team of MI5 rejects. A five-minute preview released by Town & Country magazine last week gave fans their first real look at the threats waiting in the new season, and it is not a pretty picture for the residents of Slough House.
The sixth season premiered globally on Wednesday, September 16, 2026, on Apple TV, with one new episode dropping weekly until October 21, 2026. The six-episode season adapts two of Mick Herron‘s novels, Joe Country and Slough House, marking the first time the show has combined two books into one season.
A Former Slow Horse Returns and Meets a Deadly End
The preview introduces Paul Higgins as Struan Loy, a former member of Slough House who was last seen in Season 1. Struan’s life has fallen apart since his dismissal from MI5. He now teaches karate to children, lives in a converted shipping container, and dreams of turning similar containers into residential homes.
During a grocery store visit, Struan tries to chat with a cashier and mentions he has been living in a shipping container. The cashier shows little interest, and Struan heads back to his makeshift home. Waiting for him there are two people named Jim and Jane, played by Kyle Soller and MyAnna Buring. The pair pose as investors interested in Struan’s container business idea, but the conversation turns violent. Jim and Jane attack Struan and set the container on fire with him trapped inside.
The Killers Have a List and River Cartwright Is on It
Struan is not the only former Slough House employee targeted. The teaser trailer released in August shows Jim drowning a woman who also used to work for Slough House. The two assassins are clearly working through a list, and their conversation in the preview identifies River Cartwright as their next target.
Gaby Chiappe, co-executive producer and writer for Season 6, told Town & Country about the season’s central mystery.
“We can promise thrills, twists and danger as the Slow Horses find themselves on the run. Who is after them and why is the mystery Jackson Lamb and his crew of misfits and losers need to unravel if they’re going to stay alive. And the deeper in they get, the more it seems that First Desk Diana Taverner is hiding some very dark secrets…”
River Cartwright Faces Grief and Danger at the Same Time
The premiere, titled “Circle of Life,” finds River Cartwright preparing for his grandfather David Cartwright’s funeral. David, played by Jonathan Pryce, died after a long decline due to dementia, a storyline that has been building over several seasons.
Diana Taverner, now the head of MI5, brings River to The Park to discuss funeral arrangements. The agency wants to maintain David’s cover as a Department of Transport employee, which frustrates River as he tries to grieve. Jack Lowden‘s character is described by Chiappe as “unanchored and vulnerable” following his grandfather’s death.
“He’s been losing his grandfather slowly, hasn’t he, over the past couple of seasons, to dementia? And with his grandfather gone — his mother’s never really been part of his life very much — he’s unanchored and he is vulnerable. He probably wouldn’t think of himself in that way, but I think we can see it, that he’s someone who’s trying to keep on keeping on, and he’s alone. He’s so alone.”
The funeral also brings an unexpected guest: River’s father, mercenary Frank Harkness, played by Hugo Weaving.
Lamb Investigates What MI5 Wants to Call an Accident
Gary Oldman‘s Jackson Lamb does not buy the official explanation for Struan’s death. Diana Taverner would prefer the case filed away as an accident, but Emma Flyte secretly hands Lamb the case file, knowing he will not accept that answer.
Lamb and River visit what remains of Struan’s container. The official story suggests Struan’s fractured hand, possibly from his karate work, prevented him from escaping. Lamb finds evidence that someone used a piece of wood to secure the doors from the outside. Struan did not fail to escape. Someone made sure he could not.
News of another former Slough House employee’s death gives Lamb the connection he needs. What looked like isolated incidents now appears to be a coordinated effort to eliminate people connected to Slough House.
Olivia Cooke Returns as Sid Baker After Five Seasons
Olivia Cooke is back as Sidonie “Sid” Baker, an MI5 agent who was shot in the head during Season 1 and presumed dead. The Season 6 trailer ends with Sid waiting for River at the top of a flight of stairs, greeting him with a simple “Hello River” as he stops in his tracks.
Sid’s return gives River a connection at a time when he feels isolated. Chiappe explained that Sid and Frank Harkness are characters who help River figure out who he is now that his grandfather is gone.
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Complete Cast and Global Release Details
The ensemble cast for Season 6 includes Gary Oldman, Jack Lowden, Kristin Scott Thomas, Saskia Reeves, Christopher Chung, Aimee-Ffion Edwards, Rosalind Eleazar, Joanna Scanlan, Samuel West, Ruth Bradley, Tom Brooke, Jonathan Pryce, Hugo Weaving, and Lenny Rush as a new addition. Olivia Cooke returns as Sid Baker.
The six-episode season premiered on Wednesday, September 16, 2026, on Apple TV. New episodes release weekly on Wednesdays through October 21, 2026. Apple TV is available in the United States, United Kingdom, Canada, Australia, India, and more than 100 other countries and regions worldwide. The first five seasons are currently streaming on the platform.
Also Read: Slow Horses Season 6: Director Explains Two-Book Merge as Fans Point to Royal Family Scandal Arc
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