Slow Horses season 4 review: Apple TV+ hits another home run with the most personal season yet

There's a simple reason why – it really is very, consistently good. The stories are stunningly well-adapted, the cast are superb, the action is thrilling and the pacing is impressive and tight.

Of course, all of this means it has a reputation to live up to, and each new season offers an opportunity for diminishing returns to set in. So have they?

The answer, perhaps unsurprisingly at this point, is absolutely not. The remarkable consistency of Slow Horses continues, with another season full of the thrills, the humour and the sharp storytelling that fans have come to expect from previous runs.

This season, which is based on the novel Spook Street, opens with a bombing in the centre of London, with MI5 jumping into action, and Slough House being pulled into a conspiracy which brings to light personal secrets.

That last part is key – this is, undoubtedly, the most personal season of the show yet, delving into the past of some of the central characters, and exposing key elements to their journeys.

It's what makes this season stand out right from the off, and while it would be spoiling to fun to reveal anything more at this point, it's fair to say these threads draw towards a satisfying conclusion which reshapes what we knew of multiple characters heading into future seasons.

Beyond this, in truth this season is business as usual – and that is meant as a positive. The reason Slow Horses has been such a success so far is because each new outing for the show is just as accomplished as the last, totally unique and independent, yet remaining qualitatively stable.

There are slight variations in pacing and tone here and there between seasons, but for the most part they are efficiently structured and sufficiently twisty spy stories, revelling in the genre's trappings but never fully succumbing to them or becoming clichéd.

This, in part, is thanks to how self-contained each season's story feels. As has been the case with each season so far, this new run once again tells a one-off central narrative, with just a smattering of ongoing drama and multi-season storylines to keep fans engaged long-term.

Of course, this comes directly from Herron's source material, but a lesser adaptation would have felt the need to add in more long-term plot threads and more mysteries to light up social media and online forums. Creator and showrunner Will Smith, thankfully, has listened to the adage that if it ain't broke, don't fix it, and refrains from doing so.

It leaves the show feeling like an outlier in a world of serialisation, but rather than feeling as though it has been left the behind in any way, instead it simply feels refreshing.

The cast remain a joy to watch, whether its Oldman's now iconic take on Jackson Lamb, another aspect of the show that is delightfully unchangeable, or Jack Lowden as River.

As the straight man to Oldman's Lamb, Lowden hasn't always necessarily gotten his dues for what has all along been a superb performance. This time around, it feels as though those who have failed to appreciate his excellent work across the series will sit up and take note.

Jonathan Pryce also gets more to do this time around, as we continue to follow David's mental decline and his ongoing struggle with dementia. Not only does this take the season down interesting plot avenues, it also works wonders from a character dynamic, particularly in the development of River, and allows Pryce to flex his dramatic muscles.

Meanwhile, Kristin Scott Thomas's Diana Taverner continues to be deliciously cutting, and her dynamic with James Callis's new addition to MI5, Claude Whelan, proves to be one of the season's comedic highlights.

There are plenty of other newcomers this time around too, more than is usually the case. While season 3 had Ṣọpẹ́ Dìrísù and Katherine Waterston, this run has a litany of starry new additions, from Joanna Scanlan to Tom Brooke and Ruth Bradley to Hugo Weaving.

Weaving is having a whole lot of fun as menacing new villain Frank Harkness, a mercenary with a penchant for making statements on a grand, destructive scale.

His involvement helps to add a sense of additional threat which hasn't always been quite as palpable with some previous villains, and while the action may not be quite as full-on or all-encompassing as in the latter half of season 3, there are still some terrific sequences peppered throughout.

The comedy's still wonderfully delivered and effectively deployed so as not to overwhelm the most serious moments, and the show's heart is perhaps more firmly on its sleeve than ever.

Meanwhile, the relationships between the characters only get richer and more engaging with each outing, as we get more attached to each of them and their interplay with each passing episode, all while knowing this isn't a series that's afraid to kill its darlings.

Will this winning streak continue in the already announced season 5? With other shows, that might be more doubtful, but with Slow Horses, there have no signs of decline whatsoever as the series has run on, no sense that the cast are tiring of their characters or repetitive storytelling is starting to take hold.

As long as the source material remains there for the adapting, as will be the case for quite some time, then there should be no reason that the quality will diminish.

For now, fans can just settle back and enjoy season 4, safe in the knowledge that Apple TV+ has hit another home run.

Slow Horses season 4 will stream on Apple TV+ from Wednesday 4th September – sign up to Apple TV+ now.

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