What Slow Horses Writer Mick Herron Thinks Will Happen When The Apple TV Series Runs Out Of Books

"Slow Horses" is the best spy show on TV but it started life as a series of equally excellent books by author Mick Herron. To date, the "Slough House" series as it's known, comprises nine novels and five novellas. There are also three other Herron novels that take place within the same universe as the "Slough House" series, making for an expansive literary universe from which the Apple TV adaptation can draw. But with the rate at which Apple is churning out new seasons of "Slow Horses," many are surely wondering how soon it will be before the writers run out of source material. Well, while Herron hasn't explicitly said whether he'd be open to allowing the show to chart its own course, it certainly seems as if he's open to it.

Mick Herron seems to genuinely like "Slow Horses," which thus far has remained faithful to his books while also making significant changes — most notably by featuring Gary Oldman's Jackson Lamb more prominently. During an interview for The Wheeler Centre, Herron addressed that particular change, saying:

"I'm [in the writers room] when we're discussing the adaptation process, the bits where we work out how to put a plot, much of which takes place inside characters' heads, onto the screen, translate it into action, and massively inflating the amount of time that Jackson Lamb is on-screen, as opposed to on-page, because Gary Oldman, you know? And they're paying him quite a lot of money."

Upping Lamb's screen time doesn't seem to bother Herron one bit, and the author generally seems to think of the books and the show as quite separate. All of which is to say that he might be willing to allow the writers to take his characters in their own direction when the time comes.

"Slow Horses" has what seems like a truly exhausting production schedule, with Apple TV filming seasons back to back. Season 7, for instance, had finished filming by the time 2027's Season 6 started airing, and will almost certainly premiere some time in 2027. Meanwhile, the streamer has already green-lit Season 8 which will likely debut in 2028. By that point, however, the show will have burned through all nine "Slough House" novels.

"Slow Horses" Season 6 has fixed the main issue with Season 5. By adapting books six, "Joe Country," and seven, "Slough House," the writers have created a more grounded season following the comedic tonal shift of "Slow Horses" Season 5. According to director Adam Randall, adapting two books was necessary. As he told the Radio Times, "'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." That means that after "Slow Horses" Season 6 there are only two "Slough House" novels left to adapt: 2022's "Bad Actors" and 2025's "Clown Town," which will provide the basis for Seasons 7 and 8 respectively.

During his Wheeler Centre interview, Mick Herron was asked what might happen when the show runs out of books. "I'm certainly not going to start writing any faster than I do," he said. "I think that would be a huge mistake. I'm not kept fully informed of what Apple intend, and the amount that I do know, I'm not allowed to talk about." Shortly after providing that non-committal answer, however, he seemed to imply that he wouldn't mind the "Slow Horses" writers crafting their own stories.

In his Wheeler Centre interview, Mick Herron spoke about translating his books to the screen. "I am very open to changing anything that needs to be changed," he said. "I don't mind that at all. I mean, the series, which is great, I love it. It doesn't replace the books." While he was ostensibly addressing the adaptation process, the author's comments hinted at his willingness to allow the show to chart its own course more generally. "The books are still there, so I'm happy for them to go in any kind of directions they want," he continued. "Provided they continue to get the characters right, and to get the mood right, and don't do anything which is obviously antithetical to my vision of how it should be."

For now, the TV writers won't run out of material before 2028 — by which time Apple TV may pull the plug. But the story of "Slow Horses" has been one of viewers gradually embracing the show with each new season, spurred by positive word of mouth. If that trajectory continues, by Season 8 "Slow Horses" could be more popular than ever.

With that in mind, it's reasonable to at least consider the idea of the TV writers creating their own stories to keep the show going. That said, there are five novellas yet to be adapted: "The List" (2015), "The Marylebone Drop" (2018), "The Catch" (2020), "The Last Dead Letter" (2020), and "Standing by the Wall" (2022). We here at /Film have already argued that Apple TV should turn "Nobody Walks" into a movie, but with the main novels dwindling, it might be better to use the short stories as the basis for full seasons of "Slow Horses."