The only Slow Horses Season 4 recap you need before the fifth chapter premieres this September

Apple TV’s Slow Horses is among the acclaimed spy thrillers that premiered in 2022. The show follows a group of MI5 agents who have been sent to Slough House, a place where banished MI5 agents are sent. Led by Gary Oldman’s Jackson Lamb, these agents often end up getting involved in investigations that threaten the safety of Britain.

In the previous season of the spy thriller series that premiered on September 4, 2025, Jack Lowden’s River Cartwright went to France to investigate who wanted to kill his grandfather, David Cartwright. Just like the previous seasons, the Slow Horses found themselves in a mess that had to involve the cops/Dogs, and other MI5 agents.

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River also learned about his biological father, who was linked to the assassination attempt on his grandfather. Before the release of Slow Horses Season 5 on September 24, 2025, let’s look at a recap of Season 4.

Slow Horses Season 4 recap: River went to France

In Season 4, after an assassination attempt on David, River left him in Standish’s care and went to France by taking the assassin’s identity to find out why his grandfather was attacked. He reached a remote location where he was attacked by a man and saved by another, who held him captive.

He later learned that Bertrand, the assassin’s mother, was the one who held him captive. She reveals to him that Bertrand’s father, Frank Harkness (Hugo Weaving), raised his sons from different women to be assassins.

Slow Horses Season 4 recap: Lamb learns about David’s connection to France

While River investigates, Gary Oldman's Lamb begins his own. He starts by asking questions directly to David, whose Alzheimer's has affected his memory severely. However, with his connections, he learns about David’s bagman, Sam Chapman.

Harkness has already sent his assassins to kill Chapman, but Lamb saves him once. He also learns that David had sent him to Les Arbres, in France, 30 years ago to give a mercenary group money, guns, and fake identities in exchange for a woman.

David later confesses to Lamb that the woman was his own daughter and River’s mother. Other than Lamb and River, the other members of Slough House also get involved when Harkness's men reach Slough House and cause Marcus's death.

Slow Horses Season 4 recap: River meets his biological father

The new First Desk, Claude Whelan, learns about River going to France and sends the Dogs, now headed by Emma Flyte, to capture him when he comes back to London. River learns that his mother is linked to the group at Les Abres and his caught by Flyte.

However, Harkness’s men killed four of the Dogs and took River to meet Harkness. River learns that Harkness was his father, and he wants him to join his mercenary group, but he refuses. As the Dogs approached the duo, Harkness planted a grenade on River’s clothes to cause chaos and escaped from the area.

River later helped in getting Harkness arrested. However, at the end of Slow Horses Season 4, Harkness is revealed to be blackmailing MI5 for his release. He tells them that if he is not released, the information about security agencies, including the MI5, using his mercenaries to assassinate their targets, will all be made public.

He had left letters addressed to various heads of these agencies in Molly’s house that would go online in 24 hours, revealing everything the agencies had been trying to cover up about assassinations and fake identities/cold bodies.

Keep reading Soap Central for more such stories.

Also Read: Where was The Morning Show Season 4 shot? Revisiting key filming locations of the Apple TV drama shortly before the new chapter

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