Slow Horses Season 6 Immediately Fixes The Main Problem With Season 5

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Though there are many shows like "Slow Horses" (including the new "Lanterns" series, which took considerable inspiration from the show), there's only one original. The best spy show on TV is back for a sixth season, and while it has never fallen short of greatness, there have been differing levels of greatness along the way. 

Take Season 5, for example, which focused heavily on the self-obsessed, socially inept hacker Roddy Ho (Christopher Chung). After four seasons that struck the perfect tonal balance between comedy and serious spy craft, Season 5 leant a little too heavily into the former, both in terms of its focus on Roddy and in several comedic moments that seemed like a step too far for the series. Thankfully, the Season 6 premiere has restored the balance.

"Slow Horses" Season 5 premiered in September 2025 and was based on Mick Herron's book "London Rules." As such, the writers didn't really have much choice in terms of the overarching story they told. They did, however, have a choice in how much humor to include in the episodes, and in the end, they went a little too hard in that respect. One scene stands out in particular. It sees Jack Lowden's River Cartwright and Tom Brooke's J.K. Coe accidentally kill a right-wing politician in a scene that feels like a cross between a "Final Destination" movie and "Home Alone."

Of course, Herron pulled off a tonal shift in his book series, so there was no reason why the show couldn't do the same thing. Again, "Slow Horses" has never been bad. But after Season 4 delivered some of the best episodes in the show's history, Season 5 felt like a slight downgrade. Now, it looks as though the writers are back on track for Season 6.

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"Slow Horses" Season 4 was a high point for the series, focusing on River Cartwright's struggles with his ailing grandfather and revealing major secrets about his past. Though the show maintained its all-important comedic elements, the humor punctuated what was otherwise a grounded and often moving story that represented "Slow Horses" at its best.

While "Slow Horses" Season 5 began with the most disturbing opening scene in the show's history, it very quickly lightened things up with a Roddy Ho-centric plot that often felt as though it was upsetting the careful balance of humor and drama. Then showrunner Will Smith commented on the tonal shift in "Slow Horses" Season 5, justifying it as a way of giving viewers something new following the seriousness of the previous season. "Well, we can't do [Season 4] again. It'll feel like diminishing returns," he told /Film. "And it just feels like a great thing to go in a different direction." That certainly makes sense on paper. But when it came down to it, "Slow Horses" Season 5 often felt like it was going too far in the opposite direction. 

Season 6 adapts both the sixth and seventh novels in Mick Herron's original series, "Joe Country" and "Slough House," and if the premiere is anything to go by, we're back in Season 4 territory. That's a good thing. Instead of opening with a disturbing scene, the premiere begins with Paul Higgins' Struan Loy delivering a serious speech before it's revealed that he's teaching a class of children. That didn't necessarily bode well for fans of Season 4's more serious tone, but the premiere very quickly makes up for it by going in a darker direction when Struan is burned alive inside a shipping container.

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There's one thing "Slow Horses" does better than any other spy show: It doesn't dwell on characters who have been killed off. In Season 6, however, David Cartwright (Jonathan Pryce), has passed away, and it looks as though River Cartwright will be dwelling on his grandfather's passing for some time. An early scene in which River meets with MI5 First Desk Diana Taverner (Kristin Scott Thomas) recalls the heartache of Season 4 when Taverner hands River a dossier containing photos of him and David throughout the years. Clearly the sight of happier times deeply affects River, and we're right back in business. "Slow Horses" is a human drama once again.

As things progress, the clouds literally never seem to part. Much of the episode takes place under heavy rain, and alongside the moody English churchyard scenes and the literal return of Season 4's main villain, Frank Harkness (Hugo Weaving), it's an effective way of signaling a tonal shift back towards more serious subject matter.

Interestingly enough, "Slow Horses" head writer Will Smith left the series after Season 5, so this is the first season without his input. Gaby Chiappe, who previously oversaw British crime drama "The Level," is in charge for these latest episodes, and so far it looks like it's working out. We'll obviously have to see how things play out, but at this point it seems as though "Slow Horses" has gone from good back to great.