5 things to know about the next season of Slow Horses

Slow Horses Season 4 has drawn to a close, and with Season 5 already in the can, here’s what you need to know about the further adventures of the MI5 rejects.

Slow Horses revolves around a group of spies deemed unworthy of MI5, so they’re packed off to a grotty office called ‘Slough House.’ Hence the nickname.

Run by the disheveled Jackson Lamb (Gary Oldman), the Slow Horses are considered losers and liabilities by their former colleagues. But across four seasons, the teams have successfully snuffed out multiple terrorist threats.

And while Season 4 ended in something of an anti-climax, we don’t have long to wait for Season 5, with the show set to return in 2025. Here’s what we know about what’s coming, so beware of SPOILERS ahead…

Slow Horses Season 5 is based on ‘London Rules’ by Mick Herron

Each season of Slow Horses is based on a book by author Mick Herron, and the forthcoming series is no different, being an adaptation of his 2018 novel ‘London Rules.’

John Murray Press

There’s plenty more material to turn into television as well, with the literary series spanning a number of books and novellas.

Here’s what’s previously been used as well as what’s still out there:

• Slow Horses (2010) – Season 1
• Dead Lions (2013) – Season 2
• The List (2015 novella)
• Real Tigers (2016) – Season 3
• Spook Street (2017) – Season 4
• London Rules (2018) – Season 5
• The Drop (2018 novella)
• Joe Country (2019)
• The Catch (2020 novella)
• The Last Dead Letter (2020 novella)
• Slough House (2021)
• Bad Actors (2022)
• Standing by the Wall (2022 novella)

What is ‘London Rules’ about?

The book is a post-Brexit story about a threat to the life of an MP who orchestrated the vote, and whose wife is a tabloid columnist who regularly attacks MI5 head Claude Whelan in print.

A string of apparently random terrorist attacks may also be connected to that threat, piling pressure on Whelan and the agency.

Meanwhile, the agents at Slough House are dealing with what the novel’s synopsis describes as “repressed grief, various addictions, retail paralysis, and the nagging suspicion that their newest colleague is a psychopath.”

Trailer teases assassination plot

Apple TV+

A trailer for Season 5 of Slow Horses is tagged onto the end of Season 4, and describes an assassination attempt that might be a threat to that MP’s life.

Emma Flyte (Ruth Bradley) describes it as a “destabilizing strategy,” whereby terrorists “compromise an agent, attack the village, disrupt the transport, seize the media [and then] assassinate a populist leader.”

The teaser also suggests that MI5’s Diana Taverner is starting to listen to Jackson Lamb, telling her colleagues that he knows what’s coming, and suggesting they don’t ignore him.

Ho to play a key role in Season 5

Roderick Ho (Christopher Chung) is Slough House’s technical wizard, while his somewhat eccentric behavior means he also provides comic relief.

But he hasn’t done a huge amount in the field thus far. That might change in the next season, however, as said trailer kicks off with Lamb explaining to Ho that the villains want him dead.

While in the ‘London Rules’ book, the reason Ho is a Slow Horse is finally revealed, and feeds into the main plot, suggesting that he’ll play a key role in Season 5.

The return of Frank Harkness

Apple TV+

CIA agent-turned-mercenary Frank Harkness was the big bad of Season 4, which built towards him either being captured or killed.

But while the former happened, a cache of letters containing MI5’s dirty secrets meant Harkness had a failsafe that looked like it would result in his being set free.

Therefore this major villain – who also happens to be River Cartwright’s Dad – is back on the streets. And while there’s no sign of him in the teaser trailer, expect Harkness to return, either in Season 5, or a future installment.

Slow Horses is back in 2025. Before then, check out our list of the 10 best shows streaming on Apple TV+. Or if you’re after more high-octane thrills, these are the 102 best action movies of all time.