Slow Horses season 4 review: The best show on TV ups the ante

There is no show on television right now more confident than Slow Horses, and that confidence is not misplaced. The series carries itself with an impish, slicked-hair kind of swagger that would make it insufferable to bear were Slow Horses not able to back it up. But it can, and it does. The Apple TV+ dramedy has been on a steady climb toward greatness ever since it made its quiet premiere on the still relatively new streaming platform in 2022. Since then, it has released three seasons and is on the verge of premiering its fourth. (Its rate of output alone is enough to make Slow Horses stand out in an era in which even seemingly conventional seasons of TV are taking an increasingly long time to produce.)

Last year, Slow Horses‘ propulsive, shockingly violent third season took it to greater heights than its first two. The season pushed the spy dramedy into the mainstream conversation for the first time and earned Slow Horses its only Emmy nominations to date. Less than a year later, the show is back, and it has never been in a stronger or more precarious position before. Coming off its best season to date, Slow Horses faces the challenge of proving that it can continue to deliver at the same level. Its fourth season doesn’t just do that. It also sees the series charge into more violent and personal places without ever losing the narrative and tonal sharpness that has made Slow Horses such a consistently entertaining, satisfyingly cutting thriller.

In its fourth season, Slow Horses sticks to the same proven formula as its first three, which is to say that it dedicates all of its six episodes to adapting another novel in author Mick Herron’s Slough House book series. Based on Herron’s Spook Street, the season follows Slough House head Jackson Lamb (a reliably magnificent Gary Oldman) and all of his fellow MI5 rejects as they get caught up in another conspiracy, this time involving the car bombing of a London shopping mall and a countryside murder that somehow connects to the shadowy past of River Cartwright’s (Jack Lowden) once-feared grandfather, David (Jonathan Pryce). Slough House’s impromptu investigation into the two, seemingly unrelated events is complicated by David’s worsening dementia and the introduction of Frank Harkness (Hugo Weaving), a former CIA operative whose desire to cover up his own tracks makes him a deadly nuisance.

As is usually the case with Herron’s espionage plots, Slow Horses‘ latest conspiracy is one that spirals both outward and within. Its ramifications, however, prove to be far more wide-ranging and personally impactful for everyone from River and Jackson to the ever-resourceful MI5 higher-up, Diana Taverner (Kristin Scott Thomas), her new boss Claude Whelan (a gloriously wishy-washy James Callis), and returning Slough House rejects like Shirley Dander (Aimee-Ffion Edwards) and Marcus Longridge (Kadiff Kirwan) than any of the show’s previous mysteries. Despite that, Slow Horses seems less invested this time around in drawing out the twisty nature of its newest conspiracy, and more in wringing as much tension out of MI5’s battle with Weaving’s wily Frank as it can. This results in a few set pieces, including a late-season ambush, that will leave you gasping for air.

Slow Horses season 4 continues the trend set by its predecessor by even more fully embracing the show’s action elements. Like it frequently does, the Apple TV+ drama proves that it’s capable of pulling off car chases, shootouts, and fight scenes better than other shows with considerably larger budgets. The series has proven in the past that it isn’t afraid to kill off even some of its more noteworthy supporting characters, and that lends an added sense of danger to every new confrontation and makes at least two of this season’s set pieces land with far more force than they might have otherwise. While director Adam Randall maximizes the impact of season 4’s bursts of violence, though, creator Will Smith and his team of writers never let the show get too big for its own good. Its central team’s mission this season may seem even more haphazardly executed and disorganized than usual, but Slow Horses remains firmly rooted in its protagonists’ messy, acrimonious humanity.

The show’s dialogue and comedy is as sharp-witted as ever. Generally speaking, Slow Horses doesn’t frequently venture into the same world of slapstick humor as most TV sitcoms, but there is still the spirit of a workplace comedy coursing through it. The series mines most of its humor out of the sarcastic barbs its low-level spies routinely throw at each other, and its characters are so vividly drawn that it’s just as much fun to watch Shirley and Marcus argue over the latter’s gambling addiction as it is seeing River narrowly escape yet another near-death encounter. Slow Horses‘ conspiracies may be getting more dangerous, but the show remains uninterested in sanding down the more embarrassing edges of its characters. Lowden’s River still isn’t as capable as he thinks he is, and that gives Slow Horses the space to not only trap him in more inescapable scenarios but also let him scrape by one via a motorized bicycle that barely drives faster than he runs.

The Cartwrights are very much at the center of Slow Horses season 4. This leads to some of the show’s supporting figures, like Saskia Reeves’ Catherine Standish and even — to an extent — Oldman’s Jackson Lamb, having less to do this year than in previous seasons. That’s a noticeable change of pace, but it’s ultimately the result of one of Slow Horses‘ greatest strengths: its disinterest in wasting time. The series maintains a brisk pace across its latest six episodes — propelling its plot forward in every scene and keeping its heroes constantly on the same back foot as the audience. Slow Horses prioritizes efficiency above everything else. That has led to it delivering yet another lean season of television that packs in just as much as its six episodes can contain — nothing more, nothing less — and manages to both stand on its own and continue to develop the show’s overarching narrative threads.

That balance is, perhaps, no more evident than in Slow Horses season 4’s final shot, which is itself an elegant bit of visual storytelling that simultaneously caps off the series’ latest adventure and marks another profound leap forward for its central crew of seemingly ill-fitting heroes. All in all, it’s a season that leaves you both satisfied and wanting more, which is a problem that Slow Horses, thanks to its expedient production schedule, is well-equipped to handle.

In our increasingly diluted TV environment, the race for the top spot seems to be less and less of a concern these days. But if the title of “The Best Show on TV” still even exists or matters anymore, then Slow Horses is making a consistent and increasingly compelling case for it to hold that particular crown. It may be about the shabbiest of British spies, but there’s an effortlessness behind all of its latest season’s funniest and most thrilling moments that is exhilarating to experience. No other TV show on the air right now makes greatness look as easy, and in its newest season, Slow Horses has only brought itself closer to that rare place of excellence that separates truly can’t-miss television from, well, everything else.

Slow Horses season 4 premieres Wednesday, September 4, on Apple TV+. New episodes release weekly on Wednesdays. Digital Trends was given early access to the entire season.