Slow Horses season 5 arrives on Apple TV+ tonight and here’s a handy recap of season 4 if you can’t remember everything that happened last season. And it was a LOT to be fair.

It’s been just under a year since the explosive events of Slow Horses season 4 were unveiled. Apple TV+ gave fans a new dastardly villain to loathe and another key character to mourn. Add to the mix plenty of plot twists and more MI5 corruption to try to keep up with and well, you’ll be forgiven for wanting a refresher to get you prepped and primed for your next season viewing.

Our Slow Horses season 4 recap walks you through the key storylines from the show. So you can get up to speed and excited for Slow Horses season 5.

***Warning: spoilers from Slow Horses season 4 ahead***

Slow Horses season 4 recap: Who was Frank Harkness?

Season 4 episode one started with a blast – quite literally – as MI5 and Jackson Lamb’s Slow Horses reacted to the aftermath of a suicide bomb attack on a shopping centre in central London. At first, the security services had little information on the culprit who claimed responsibility behind the attack – a man called Robert Winters.

But, as the season continued, we learnt that Winters was one of many young men turned mercenaries groomed by Frank Harkness (Hugo Weaving). Frank was an ex-CIA operative who was dismissed from duty decades prior for embezzlement and torture crimes.

During a trip to Lavande in France, River Cartwright (Jack Lowden) discovered that Frank had been breeding his own army of assassins. Frank had been fathering sons by different mothers and training them up to carry out ruthless terrorist activities (while he cashed in considerably). Winters was one such ‘soldier’, as was the deceased Bertrand – the man killed by David Cartwright (Jonathon Pryce) earlier in the series. 

It turned out that River’s grandad David had history with Frank. In fact, so did River – although he didn’t know it yet. We learnt that Frank was actually River’s biological father. River’s mum – David’s daughter – was one of the women who was duped into joining Frank in France and providing him with a son for his services. Back when David was running MI5, he sent his fixer Sam Chapman to Lavande with weapons, cash and MI5 cold body identities in exchange for his daughter’s safe return.

Slow Horses season 4 recap: Who is River Cartwright’s dad?

In the season 4 finale, River came face-to-face with his real dad after being kidnapped by another of Frank’s mercenaries, Patrice. River was aware of Frank’s identity, despite his family’s cover-up, sarcastically greeting him with a “hello dad”. The reunion was anything but emotional though, with Frank showing little feeling or sympathy for River’s mother or his parental absenteeism. He instead cut straight to the chase offering River the chance to join his assassin army. Of course, River declined.

Unbeknown to Frank, River had had colleague Louisa and a team of officers tracking their location. However, an MI5 crack squad with instructions to shoot River complicated matters and Frank escaped shortly after planting a grenade on River. Louisa was able to get to the grenade in time, saving River and sending it into the nearby canal instead. 

A high-intensity chase followed with River running after Frank, before catching up to him at St Pancras train station. Frank admitted defeat and handed himself in to MI5. He then underwent thorough questioning by Diana Taverner (Kristin Scott Thomas). However, his detention didn’t last long thanks to a follow-up failsafe plan. 

The Park’s cover-ups continued

It’s MI5 agent Giti Rahman (Kiran Sonia Sawar) who did some digging into Frank Harkness and his killer offspring. Her intel led Diana and Claude Whelan (James Callis) to link the MI5 cold body identities to Frank and stage a cover up, since the identities connected MI5 to a number of worldwide assassinations and terrorist activity. 

It’s this link that ensured Frank was release in the finale. Jackson Lamb showed Diana letters that claimed MI5 used his services to do their “dirty work”. Frank threatened the letters would go live on the internet if he wasn’t released.

Separately, Standish’s replacement Moira Tregorian (Joanna Scanlan) unveiled another cover-up and the reason behind her demotion to Slough House. After using her contacts at the Park to help the Slow Horses, Ho (Christopher Chung) hacked into some confidential files. He found that she’d been moved when Claude stepped up as Chair. Armed with the evidence of his late night activities, she confronted Claude about his Galahad identity and street-based soliciting. She was successfully able to negotiate her old job back with a pay rise. 

Slow Horses season 4 recap: RIP Marcus, welcome Coe

Assassin Patrice arrived at Slough Horse under orders from Frank to kill Jackson. Minus River and Louisa, the remaining Slow Horses fought hard to stave off Patrice. Sadly, Marcus was on the receiving end of one of his bullets and died. 

Following Marcus’ murder, Patrice was captured and chained up to the radiator in Jackson Lamb’s office. A devastated Shirley tried to kill him but was talked out of it by Coe. After she left, Coe – who had been pretty quiet until that point – unflinchingly finished off the job himself.

JK Coe (Tom Brooke) was a Slough House newcomer in season 4 who quietly loitered in the corner. Though we did get hints of his backstory. Shirley’s handcuffing prank on Roddy Ho triggered Coe into an episode, which revealed his PTSD diagnosis. During a previous assignment he’d been handcuffed and tortured with an electric carving knife. We look forward to seeing and learning more about Coe in Slow Horses season 5.

Read More: I Fought the Law on ITV: Where is Julie Hogg’s killer Billy Dunlop now and is he still in prison?

Slow Horses returns to Apple TV+ on Wednesday September 24, 2025.