Mick Herron on Slow Horses: Gary Oldman’s Jackson Lamb Adds Emotional Depth Not Found in the Novels

Series author Mick Herron has revealed that Gary Oldman’s acclaimed depiction of the shambolic MI5 reject Jackson Lamb is straying further from the original literary character as Slow Horses returns for its sixth season on Apple TV+. The new season, which debuted on September 16, 2026, has received mixed reviews from critics, with some major publications noting a change in tone of the spy thriller.

Slow Horses Season 6 arrived on Apple TV+ on September 16, 2026. Gary Oldman’s portrayal of Jackson Lamb “is diverging” from the book, with visible emotional reactions, series author Mick Herron told The Guardian. But the sixth season has received a mixed critical response, with some reviewers pointing out that while the series is still slick and confident, it is becoming more predictable.

The sixth season of the Apple TV+ espionage series is based on two of Mick Herron’s Slough House novels: Joe Country and Slough House. The season continues with the disgraced MI5 agents banished to administrative purgatory, led by the foul-mouthed Jackson Lamb, who seems disengaged.

In the opening episode, Olivia Cooke reprises her role as Sid Baker, who was presumed dead after being shot in the head in the first season. Her return also brings back complicated dynamics with Jack Lowden’s River Cartwright, a key relationship that Herron has used in the past to highlight the bleak, unheroic reality of the Slough House milieu.

In a September 16, 2026, interview with The Times, Mick Herron spoke about the long-standing differences between his literary creation and the television adaptation. Herron is an executive producer and consults from time to time, but has long seen the television series as separate from his books.

However, Herron did note a specific shift in Oldman’s performance in the latest season. “I think I’m probably right in saying this is where Gary’s performance, Gary’s version, if you like, of Jackson is probably starting to diverge from mine,” Herron stated.

Jackson Lamb rarely gives an observable emotional response in the novels, he said. The TV series, however, has started to tease out moments of real concern or shame from the character, especially in his dealings with Catherine Standish, played by Saskia Reeves. “Whereas Gary… I think it must be necessary to do that on screen, otherwise you are just portraying an automaton, I suppose,” Herron added, explaining that depicting Lamb as a pure monster or cartoon would be a disservice to an actor of Oldman’s caliber.

The reception to the sixth season has been mixed. The show still has a solid overall rating on aggregate platforms, but some prominent outlets are expressing fatigue with the series’ established formula.

A recent review in The Guardian ran with the headline “it gets harder to enjoy Gary Oldman’s spy thriller every year”. The review called the latest season “reliable” and “predictable,” and said the show has been remade into a more traditional thriller than its earlier, more subversive seasons. The review recognized that Slow Horses was still ‘slick and confident enough’ to keep its audience, despite the criticism.

Other outlets, though, have praised the season, with Inverse calling the series “hitting a new peak,” and still humming with suspense and entertainment value.

The gap between Herron’s literary Jackson Lamb and Oldman’s television version reflects a familiar problem with long-running book-to-screen adaptations. As a TV show matures, it’s natural for actors to add depth to roles that might not be on the page. For Slow Horses, this evolution raises questions about how faithful the show can be to the darker, future Slough House books if the lead becomes more and more sympathetic.

Season 6’s mixed critical response also suggests the show is reaching a level of maturity where it may struggle to sustain its initial subversive edge amid more conventional television thriller expectations.

New episodes of Slow Horses Season 6 will continue to drop weekly on Apple TV+ until late October 2026. Apple has already recommissioned the series for an eighth season, meaning the Slough House team will be on screen for the foreseeable future. Herron’s upcoming Slough House novella collection, Watch the Quiet Snow, is scheduled for publication on October 22, 2026, providing additional source material for future television adaptations.

What is Slow Horses Season 6 based on?
Season 6 is largely adapted from two of Mick Herron’s novels, Joe Country and Slough House.

Did Mick Herron criticize Gary Oldman’s acting?
Nope. Oldman was a “fine an actor,” Herron said, and he acknowledged that observable emotional responses are likely necessary for the screen to keep the character from becoming a “automaton.”

Is Slow Horses finishing after Season 6?
No. Apple TV+ has renewed Slow Horses for a seventh and eighth season, which are already in various stages of production.