Slow Horses is returning for its sixth season with a major change. For the first time in the show’s history, the Apple TV spy drama is adapting two novels in a single season. Director Adam Randall has explained the creative decision behind merging Mick Herron’s sixth and seventh books, Joe Country and Slough House. However, a section of fans believes the real reason is a controversial storyline involving the royal family that the show may have chosen to avoid. The new season premieres on September 16, 2026, with Gary Oldman returning as the unforgettable Jackson Lamb.
Why Slow Horses Season 6 Combines Two Books
Adam Randall, who also directed Season 4, spoke exclusively with Radio Times about the decision to merge two novels for the first time. He explained that while both books are strong, one of them did not provide enough material for the show’s main characters.
“With season 6, we decided that we needed to combine two books, which was the first time we’d done that,” Randall said. “So I read them both. I read Joe Country and Slough House. They’re both fantastic. Joe Country would make the most amazing film, but it was felt that there was not a huge amount of story for a number of our characters.”
Randall further clarified that Diana Taverner and Jackson Lamb do not have substantial roles in Joe Country alone, making it difficult to build a full season around that book.
“Taverner’s not in it a great deal, Lamb hasn’t got a huge amount to do, so it was sort of the decision to combine them and find a way for them to work together. But then we had the opportunity to draw on both of them throughout the process, which was really fortunate.”
The official synopsis for Season 6 aligns more closely with the plot of Slough House, the seventh book.
“Season 6 sees the Slow Horses on the run as Diana Taverner embroils them all in a fatally high-stakes game of retaliation and revenge.”
What Happens in Joe Country and Slough House
Joe Country, published in 2019, follows a missing teenager named Lucas, River Cartwright, and a former spy named Frank Harkness. The story involves a senior member of the royal family who is linked to a brutal incident with a young woman. Lucas witnesses the incident and later tries to use it for blackmail. Instead of meeting his demands, the royal’s associates send mercenaries after him, which eventually pulls the Slow Horses into the case. The book also introduces Lech Wicinski, an MI5 analyst who finds illegal material on his work laptop and believes he is being framed.
Slough House, the seventh book, sees Diana Taverner seeking revenge after a poisoning attack tied to Russia. She partners with Peter Judd. Meanwhile, Jackson Lamb’s team discovers they have been wiped from MI5’s records, and former members begin dying in unusual circumstances.
Apple’s official premise for Season 6 confirms that the agents are on the run while Taverner involves them in a dangerous game of retaliation and revenge, connecting elements from both novels.
Fans Say Royal Family Scandal Is the Real Reason
While the director cites narrative balance as the reason for merging the books, fans on Reddit and other platforms have offered a different theory. A widely discussed post on the r/SlowHorses subreddit speculated that the show combined the books to avoid the royal family scandal storyline from Joe Country.
One Reddit user pointed to three possible reasons behind the merge:
“1. The Lech story line as an accused and subsequently scared p***o not appropriate for general public viewing 2. Staying away from the covering up of a Royal’s scandalous behavior 3. An extended snowy rural chase in Wales not practical to film in the UK”
The royal sex-scandal plotline from Joe Country has indeed been removed from the TV adaptation, as noted in early reviews. A Radio Times review of Season 6 confirmed that the storyline has been “nixed, perhaps to avoid potentially controversial subject matter.” The same review also noted that Lech Wicinski is absent from the season.
Apple TV has not officially commented on why these specific storylines were left out. The streaming platform has only shared the director’s explanation about character balance.
Release Schedule and Where to Watch
Slow Horses Season 6 premieres globally on Wednesday, September 16, 2026, on Apple TV. The season consists of six episodes. The first episode drops on the premiere date, followed by one new episode every Wednesday until the finale on October 21, 2026.
The complete first five seasons of Slow Horses are currently streaming on Apple TV.
Cast Returns and New Additions
The ensemble cast for Season 6 includes several familiar faces and one notable newcomer.
Returning cast members include:
- Gary Oldman as Jackson Lamb
- Jack Lowden as River Cartwright
- Kristin Scott Thomas as Diana Taverner
- Saskia Reeves as Catherine Standish
- Christopher Chung as Roddy Ho
- Aimee-Ffion Edwards as Shirley Dander
- Rosalind Eleazar as Louisa Guy
- Joanna Scanlan as Moira Tregorian
- Samuel West as Peter Judd
- Ruth Bradley as Emma Flyte
- Tom Brooke as J.K. Coe
- Jonathan Pryce as David Cartwright
- Hugo Weaving as Frank Harkness
Olivia Cooke is reprising her role as Sidonie “Sid” Baker, last seen in Season 1. Lenny Rush joins the cast as a new character.
MyAnna Buring and Kyle Soller also appear in the season as new characters targeting Slough House agents.
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What Critics Are Saying
Early reviews for Slow Horses Season 6 have been largely positive. Empire called it “a masterclass in brutal thrills and caustic comedy,” praising the show’s ability to balance dark espionage with sharp humor. The review noted that the season is “particularly bruising” as a pair of killers begin murdering past and present “horses” one by one.
The review also highlighted the return of Olivia Cooke as Sid Baker, describing it as “the unexpected return of Sid Baker, last seen seemingly dying in Season 1.” Hugo Weaving re-enters the story as Frank Harkness, River’s father, who is described as “River’s worst-father-ever.”
Radio Times noted that the season features “another high-wire act of laughs and thrills,” though it mentioned “the occasional misstep” and confirmed the absence of the royal family plotline and the Lech Wicinski character.
Also Read: Slow Horses Season 6 Release Schedule: Every Episode Date and What Time New Episodes Drop
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