There have been a plethora of great spy shows in the 21st century from Spooks to The Americans. Few, however, have been as successful as Slow Horses, an adaptation of Mick Herron’s ongoing Slough House series of novels, currently nine books deep and set in London.
Slough House is basically a dumping ground for spooks that MI5 considers no longer viable. And they all seem to have character quirks – defects, even. For the Slow Horses, the spymaster is Jackson Lamb (Gary Oldman) whose lifestyle and manners are perhaps his biggest flaws. There’s River Cartwright (Jack Lowden), a promising spy who has messed up a major mission, and whose vanity is there to trip him up. Another key character is Roddy Ho (Richard Cheung), the hacker and cyber espionage expert with a legendary lack of self-awareness. Catherine Standish (Saskia Reeves), assistant to Lamb, is a recovering alcoholic.
But this is a programme that proves that unloved doesn’t mean unloveable, and being written off once doesn’t mean you’ll never be great at what you do. Indeed, unhindered by the egos, internal and external politics, and bureaucratic ineptitude of mainstream MI5 over at The Park, the Slow Horses are often two steps ahead of the conventional spooks.
Perhaps you now imagine the characters from the show while reading the books; perhaps not. But what the show does provide is action and momentum that can be hard to conjure in words alone. The chases, the fights, the unorthodox set pieces and improvised weapons – they give the stories a whole new level of excitement. Meanwhile, the superb acting makes the most of Mick Herron’s irreverent humour with the addition of that crucial element: comic timing. At a deeper level, the author’s picking apart of acting in the national interest, what it entails and what, indeed, the national interest is these days, continues to make the show tick.
Herron himself is involved heavily in the production and has remarked on multiple occasions how satisfied he is with the adaptation. It has proven so successful that Apple has brought his earlier series to life in Down Cemetery Road, with Emma Thompson and Ruth Wilson the leads.
Time to look at the series in more detail. It’s immediately obvious from Mick Jagger’s theme music, that while spying is a strange game, this show means business.
Season One (June 2022)
The first book, Slow Horses (2010) might not be the most acclaimed novel in the series but every franchise has to start somewhere and the first season of the show introduces us to the Slough House crew and Mick Herron’s take on MI5. River Cartwright is involved in a botched training exercise and soon finds himself at the mercy of Jackson Lamb, a slovenly individual who has genius lurking behind his dishevelled appearance.
The titular crew group of spooks become embroiled in a wider crisis instigated by MI5’s upper echelons, namely Diana Taverner. A kidnapping goes sideways and it is up to Slough House to save the day. It’s high stakes and a race against the clock, really setting the tone for the seasons to come. Unlike other shows it seemed to arrive with a sense of identity built in rather than finding its feet, buoyed of course by the unrivalled ensemble cast.
Season Two (December 2022)
A dead former agent, found at a bus station, triggers events in the show’s sophomore season. There is clearly more to this death than meets the eye, sending Lamb on the warpath. This season is tighter, with River playing detective in a sleepy village in the Cotswolds that might be housing dark secrets and danger to the nation from bad actors. We are introduced to several new occupants in Slough House in fan favourites Marcus and Shirley while we say goodbye to others.
Based on Dead Lions, it came out just months after the first season but having two seasons in six months didn’t dent the show’s momentum, if anything it simply helped reinforce how strong the response was building the word of mouth.
Season Three (November 2023)
We open with an action-packed overseas mission in Istanbul, which is about as globe trotting as Slow Horses gets. Of course things quickly go sideways, kickstarting a revenge mission against MI5 and The Park. One of the Slow Horses is kidnapped in the proceedings, prompting Lamb to bay for blood because no one messes with his Joes. The plotting and layers never prove to confusing as showrunner Will Smith and his team peel back the layers to a conspiracy, delivering visceral action and laugh-out-loud moments.
The climactic action is some of the best you’ll find, giving each member of Slough House a moment to shine and prove they’re not the outcasts the rest of MI5 thinks they are. This season, based on Real Tigers, captures the grey nature of the intelligence community, our supposed goodies sometimes amplifying tension and causing headaches for Slough House.
Season Four (September 2024)
We finally learn more about River Cartwright’s past, but it’s not quite the reunion he had in mind in this adaptation of Spook Street. This is another action-packed entry that sees Cartwright junior jet off to France in search of clues. It also sees the most prominent role in the show for his grandfather, David (Jonathan Pryce), at the heart of proceedings. Things get more John Wick-like with indestructible assassins on the rampage but the show manages to make it remain believable and keep the audience invested; other shows might struggle to pull it off in a convincing way.
Hugo Weaving is delightfully menacing as Frank Harkness, a former US intelligence agent, now running amok and causing chaos. Ruth Bradley is another welcome addition as Emma Flyt, former Met Police, now running the security detail for the service The Dogs, who seems far more agreeable than her predecessor. James Callis is also a bumbling treat as the new head of the service, Claude Whelan (James Callis), getting more out of his depth with every passing moment.
Season Five (September 2025)
This is where the show starts to depart from the books a little more, with season five based on London Rules. We open with a shooting during the London mayoral election, and across London far-right politician Dennis Gimball, environmental activist and Islamists are all stirring up trouble. Tech wizard and oddball Roddy Ho seems to have found love at last but is his new girlfriend Tara all that she seems? Of course this being Ho, his love life causes all sorts of trouble for MI5. Chris Chung is on top form, relishing in the larger role for his larger than life character.
With terror incidents happening across London and the team stretched to the breaking point, danger seems to lurk around every corner, and a real sense of desperation sets in as the antagonists start to use the service’s own strategies against them. This was the final season from showrunner Will Smith and a fine, Emmy-winning way to bow out and usher in a new era.
Season Six (September 2026)
This season is a departure from the norm, based on the novels Joe Country and Slough House, which are six and seven in the series. Someone is killing former members of Slough House, while the incumbent team have all been struck from the MI5 payroll. River is mourning the loss of someone close, while several people from his past turn up, albeit in very different circumstances. Although this series takes more radical departures from the novels, the spirit of Herron’s world is still intact. Some deaths are altered and characters’ arcs do shift, but the writers largely do an admirable job making it work and combining the disparate stories.
With the two books being combined, this is the most frenetic the show has been to date, upping the ante with multiple members of the crew on the run and facing extreme danger. Diana Taverner, meanwhile, is finally First Desk at The Park and looks to have got herself in a spot of hot water even she might struggle to extricate herself from.
Also see our guide to the Slough House novels by Mick Herron.
