The sixth season of the espionage drama Slow Horses marks a notable shift in tone and creative direction following the departure of longtime lead writer Will Smith, whose previous work on The Thick of It and Veep contributed to the series’ distinctive blend of sharp humor and suspense. Under new writer Gaby Chiappe, known for The Level and The Beast Must Die, the show adopts a more conventional and serious thriller approach, moving away from the droll satire that had become its hallmark.

Slow Horses centers on the staff of Slough House, a demoralizing division of MI5 where disgraced and underperforming agents are relegated to mundane tasks rather than dismissed outright. The protagonists, led by field operative River Cartwright (Jack Lowden), navigate a world in which they repeatedly outshine their elite peers despite their apparent incompetence. The interplay of humor and espionage has helped audiences accept the series’ improbable survival scenarios, but that balance appears to be strained this season.

The previous season saw a diminished storyline involving generic terrorist threats linked to British foreign policy, alongside diminishing returns from characters initially introduced as comic relief. Notably, Roddy Ho (Christopher Chung), once a popular source of snark, was elevated to a central role that many viewers found less compelling. Gary Oldman’s portrayal of Jackson Lamb, the abrasive and physically unappealing Slough House leader, also showed signs of creative exhaustion, losing some of the vitality that made the character compelling.

Season six initiates its narrative with a deadly plot targeting former Slough House members from early seasons. This includes the brief return and subsequent death of Struan Loy (Paul Higgins) amid bleak settings characteristic of the series, such as a shipping container isolated on estuary mudflats. As two highly skilled assassins, played by MyAnna Buring and Kyle Soller, continue their lethal campaign, the remaining Slough House personnel find themselves on the run.

The storyline also reintegrates several familiar faces whose exits in previous seasons appeared conclusive. Rosalind Eleazar returns as Louisa, Joanna Scanlan resumes her role as Moira, and Hugo Weaving reappears as Frank, a morally ambiguous mercenary revealed to be River Cartwright's father—an arc some considered resolved by season four. While their returns are generally well-received, the reliance on established characters may signal creative challenges for the show.

At its core, the season's plot revolves around an extended pursuit, with the protagonists often narrowly escaping due to the surprisingly fallible skills of their pursuers. The show’s trademark witty banter is less frequent, and geopolitical elements, aside from some references to Russia, are subdued. Despite casting talented actors in key antagonist roles, the series offers limited development of these characters, diluting the overall impact.

Slow Horses remains a polished production bolstered by strong performances, including Lenny Rush, whose role as a civilian caught in the ensuing turmoil adds depth to the ensemble. Nevertheless, the series appears to be grappling with creative fatigue, raising questions about its long-term trajectory.