Author Drops Bombshell: Slow Horses Season 5 Makes Major Departures From the Books
Mick Herron isn’t a purist: he loved the deviations from the novel — and engineered a few himself.
Slow Horses is back next week, and yes, the new season is based on the fifth book. Also yes: it messes with the book. In a good way.
Book vs show: same vibe, different route
Season 5 pulls from Mick Herron’s fifth Slough House novel, London Rules, but readers should expect detours. Herron was at a BFI screening for the new season and told RadioTimes he thinks the whole thing is fantastic. He was looped in early, talked through the tweaks, and even kicked off a few of them himself. He’s not precious about plot, as long as the people feel right.
"It’s done with such enormous fidelity to the characters – not to the plots, which is not important to me, but to the characters, which is important to me – that the difference is purely one of transmission. [Showrunner Will Smith] totally, as do the other writers, gets the mood and tone of the books."
That Will Smith note is a bit of inside baseball: he’s the British writer running the show, not the movie star. And Herron’s main point stands — character over plot. So the bones are familiar, but the muscles flex differently.
So what is season 5 actually about?
Slough House’s chaos magnet Roddy Ho suddenly has a stunning new girlfriend, which sets off alarm bells for the team. Meanwhile, London starts throwing up a string of weird, seemingly unrelated incidents. It falls to the Horses to connect the dots. And as Jackson Lamb would remind everyone, the London Rules still apply: cover your back.
Season 5 essentials
- Premiere: September 24, 2025 on Apple TV+
- Source material: London Rules (book 5), with deliberate departures approved by Herron
- Returning cast: Gary Oldman, Jack Lowden, Kristin Scott Thomas
- New face: Nick Mohammed as Zahar Jaffrey, the London Mayor
- Plot spark: Roddy’s too-good-to-be-true romance + bizarre citywide incidents = Slough House homework
The Mayor, the comparisons, and the reality
Nick Mohammed’s character will inevitably remind people of Sadiq Khan. Mohammed has already waved that off, saying the Mayor is drawn from lots of different politicians, not a one-to-one lift.
Bottom line
If you’re looking for a page-perfect translation of London Rules, that’s not this show — on purpose. Slow Horses stays loyal to the characters and the tone, then finds its own way to the finish line. Sounds like the London Rules to me.