Key Takeaways
Season 4 of Slow Horses reveals intense plot twists and character developments
The final episode of Season 4 ends in tragedy
The season 5 teaser trailer hints at more action, assassinations, and relationship drama
Apple TV+ has some genuinely brilliant shows, many of which go a little under the radar, on account of being on a streaming service that’s not as popular as options such as Netflix and Disney+. Ted Lasso is one of the rare shows that has been a breakout hit for Apple TV+, but shows such as the excellent Severance , Silo, and For All Mankind aren’t as popular as they deserve to be.
Another hugely underrated show is Slow Horses, which is one of the best shows on the streaming service. It tells the story of Slough House, a department of MI5 where the worst agents and biggest misfits are sent to keep them out of the way of the real work. They work under Jackson Lamb, a grotesque and flatulent man played to perfection by Gary Oldman (Bram Stoker’s Dracula, The Fifth Element). In a pun on the name of their location, these misfits are known as the Slow Horses.
The first three seasons of Slow Horses have been truly excellent, each containing its own self-contained central story line. The teaser trailer for season 4 indicated that one of the Slow Horses would die, but which one would it be? Here’s what happened at the end of Slow Horses season 4.
Season 3 of Slow Horses ended with the First Desk of MI5 being outplayed by her second in command, Diane Taverner (Kristin Scott Thomas, Darkest Hour) who is after the top job. However, at the start of season 4, things haven’t quite gone to plan. Taverner is still Second Desk, and there’s a new face in charge of MI5.
The new First Desk is Claude Whelan, an inept pencil pusher played deliciously by James Callis (best known for playing Gaius Baltar in Battlestar Galactica). There’s also another new face at MI5; Emma Flyte, played by Ruth Bradley (Ted Lasso) is the new Head of Security.
The new First Desk is Claude Whelan, an inept pencil pusher played deliciously by James Callis (best known for playing Gaius Baltar in Battlestar Galactica).
Flyte is dropped right into the action at the start of season 4. River Cartwright (Jack Lowden, The Lord of the Rings: The Rings of Power) visits his grandfather, David Cartwright (Jonathan Pryce, The Crown) who is suffering from dementia. In his confused state, the elder Cartwright becomes convinced that the man claiming to be River is actually someone who has been sent to kill him, so he shoots River dead. Flyte is sent to investigate, and has her first run-in with the head of the Slow Horses, Jackson Lamb.
Lamb confirms that the body is River Cartwright, but we don’t have to grieve for long. It soon becomes clear that River is still alive and well, and that the dead body is someone who looks remarkably like him who was sent to kill David Cartwright. River travels to France using the dead man’s passport to try to find out why, while Whelan and Taverner deal with the aftermath of a bombing at a shopping center.
River’s trip to France uncovers information about the man who is now lying dead in his grandfather’s bathroom. He meets the dead man’s mother, who explains that her son is the result of an affair with an American man (Hugo Weaving, The Matrix) who then abandoned her but took her son with him.
Over the course of season 4, we discover that this man is Frank Harkness, an ex-CIA agent who has been trying to build the ultimate murder squad by creating an army of unidentifiable hitmen with fake identities from his own children. The bomb at the shopping center turned out to be a final “screw you” to his father from one of these children, by turning what was meant to be a surgical assassination into a major incident.
Harkness is trying to kill anyone who knows about his operation, which includes David Cartwright, his former employee “Bad” Sam Chapman, and now River himself.
Further investigation uncovers the truth; back when he was working at MI5, David Cartwright sent Harkness money, weapons, and fake identities in exchange for the return of a woman who was living in France with Harkness. Lamb discovers that the woman was none other than David Cartwright’s daughter, and River’s mother. Harkness is trying to kill anyone who knows about his operation, which includes David Cartwright, his former employee “Bad” Sam Chapman, and now River himself. At the end of episode 5, River is captured by one of Harkness’ team and thrown into the trunk of a car.
River is taken to meet with Harkness, and what he has begun to suspect is confirmed to be true. David Cartwright’s daughter was in a relationship with Harkness. When she was returned to England in exchange for the guns and fake identities, she had in fact been pregnant by him. Harkness is River Cartwright’s dad.
Harkness tries to convince River to join him, having been impressed with his resourcefulness. River manages to alert Slough House, and during a confrontation, Harkness escapes.
Meanwhile, another of Harkness’ sons is aiming to finish the job on David Cartwright, having obtained his location from “Bad” Sam Chapman before killing him. This leads to a showdown at Slough House, with Lamb’s secretary Catherine Standish (Saskia Reeves, Luther) and two of the Slow Horses, Shirley Dander (Aimee-Ffion Edwards, Skins) and Marcus Longridge (Kadiff Kirwan, Chewing Gum) his only protection. They manage to neutralize the assassin, but at a terrible cost; Marcus Longridge is killed in the struggle.
The show ends with two emotional scenes. In the first, River is forced to make the difficult decision to place his grandfather into a nursing home.
River chases Harkness to the train station where he is taken in by MI5. It all seems a little too easy, which of course it is. Harkness has left a “fail-safe” of several letters that will be released on the internet unless he is released. The letters make clear that MI5 and other governments have been using Harkness’ hit squad for years to do their dirty work. MI5 has no choice but to let Harkness go.
The show ends with two emotional scenes. In the first, River is forced to make the difficult decision to place his grandfather into a nursing home. Afterward, he is met at the pub by Lamb, where the two share a drink in silence in an incredibly rare example of Lamb showing kindness directly to one of this team.
River Cartwright and Louisa Guy in Slow Horses season 4
There’s a lot to unpack from the short trailer that follows the end of the final episode of season 4. The trailer starts with a masked assassin trying to kill Roddy Ho (Christopher Chung, Waterloo Road), the socially inept IT expert from Slough House. Flyte describes a destabilization strategy that culminates in the assassination of a populist leader, while everything she describes plays out on screen.
Whelan is still First Desk, with Taverner still his second in command, and they are seen discussing the fact that Lamb knows what’s coming next and that he has more field experience than anyone else at MI5. And perhaps most intriguingly, River is seen clumsily attempting to kiss fellow Slow Horse Louisa Guy (Rosalind Eleazar, Class of ’09) who does not look too happy about it. There’s no sign of Harkness, but it seems unlikely that he won’t make a reappearance at some point in the remainder of the show.
There’s no confirmed date for when season 5 of Slow Horses will be released, but based on the pattern from previous seasons, which have dropped towards the end of each subsequent year, we should expect season 5 to arrive in late 2025.
