Slow Horses' Original Writer Walked Away After Season 5. Season 6 Just Became the Show's Best-Reviewed Season Yet

Handing a beloved show to someone new is one of the riskiest moves in television, and it rarely goes cleanly. Ask anyone who watched a favorite series limp through a showrunner change. So there was real reason to worry when Will Smith, the writer who'd shaped every one of Slow Horses' first five seasons practically by himself, stepped away at the end of Season 5. What actually happened next is the kind of outcome that almost never happens: Season 6 didn't just hold the line, it became the best-reviewed season the show has ever put out.

A handoff nobody was sure would work

Slow Horses doesn't run with a traditional showrunner, but Will Smith had functioned as its de facto captain since it premiered in 2022, writing the scripts that turned Mick Herron's Slough House novels into one of the more consistently acclaimed shows on television. His exit after Season 5, described at the time as coming "with great sadness on both sides," left the production searching for someone who could keep the tone intact without simply copying him. They landed on Gaby Chiappe, the writer behind The Beast Must Die and The Level, who stepped into the lead writer role for a production of a size and profile she'd never handled before. "It was an amazing opportunity," Chiappe said of taking the job, before admitting in the same breath that it was "obviously nerve-wracking."

What's notable about how Chiappe talks about the handoff is that she doesn't claim to have replaced Smith so much as absorbed one piece of what he did. "I don't feel like I stepped into Will's shoes," she said. "I took over one aspect of the many things Will was doing... in the middle of the process, there was a Will-shaped hole." Gary Oldman, who's played Jackson Lamb since the first episode, called the transition "pretty seamless," crediting five seasons of established tone and Herron's source novels for giving Chiappe a solid foundation to build from rather than a blank page. "Gabby came in and took the helm and was terrific," Oldman said. It's a small detail, but it matters: the show's continuity survived not because nothing changed, but because everyone involved was honest about what a partial handoff actually looks like.

Breaking a format that had worked for five seasons

Chiappe's first big decision wasn't stylistic, it was structural. Every previous season of Slow Horses had adapted exactly one Herron novel across six episodes — Slow Horses, Dead Lions, Real Tigers, Spook Street, London Rules, one book per year, like clockwork. Season 6 broke that pattern for the first time, weaving together Joe Country and Slough House, the sixth and seventh novels in Herron's series, into a single run. Executive producer Doug Urbanski explained the thinking plainly: "We thought the two books each were thin enough" to justify combining them, rather than stretching either one past what it could naturally support. It's the kind of call that could easily read as a cost-saving shortcut from the outside, and critics went in expecting exactly that kind of strain.

Instead, reviewers came away describing a season that felt more serialized and more confident than anything the show had tried before, not less. One review noted there was "no hint that this story has been Frankenstein-ed together," with the two books' elements blending into "an unbroken and complete narrative that keeps upping the ante." The season also brought back Olivia Cooke as Sid Baker, a character fans had believed dead since being shot in the head at the end of Season 1, alongside a returning ensemble of Jack Lowden, Kristin Scott Thomas, Saskia Reeves and Christopher Chung, plus newcomer Lenny Rush as a teenager who stumbles into MI5's orbit. Betting on continuity, in other words, meant leaning harder into the show's own history rather than starting over — a choice that only works if the people making it actually trust the audience to keep up.

An Emmy two days early, and a future already locked in

The timing around all of this ended up almost theatrical. On September 14, two days before Season 6 premiered, Slow Horses won the Emmy for Outstanding Directing for a Drama Series, with Saul Metzstein taking the trophy for "Scars," the Season 5 finale — a genuine upset, by Variety's own account, over more heavily favored nominees tied to Pluribus and The Pitt. It marked the third straight year the show had walked away with either a writing or directing Emmy, following Will Smith's writing wins in 2024 and 2025. The show didn't sweep the night; The Pitt took Outstanding Drama Series and Noah Wyle repeated as lead actor, and Slow Horses' nine total nominations, including nods for Oldman, Lowden and Jonathan Pryce, didn't convert into the bigger prizes. But craft-category wins three years running is its own kind of statement, especially for a show that's never been the loudest name in its category.

Then came the reviews, and then came the next commitment. Season 6 opened to a 100% Tomatometer score, its third perfect season after Seasons 2 and 4, pushing the show's overall six-season average to 98% with critics and 88% with audiences — the best Rotten Tomatoes record of any Apple TV series with five or more seasons to its name. Apple didn't wait around to capitalize on any of it: alongside the Emmy win, the streamer confirmed a Season 8 order, a six-episode run adapting Clown Town, the ninth Herron novel, with Oldman and Scott Thomas both set to return for what's being billed as Lamb and Taverner's most explosive confrontation yet. Season 7 was already locked in before any of this happened. By the time viewers pressed play on Season 6's first episode, the show's next two years were already spoken for.