The latest season of Slow Horses, the popular Apple TV+ spy thriller based on Mick Herron’s novels, has come to an end. Season 4 has run for six fast-paced weeks, bringing with it lots of surprises, intense action, and deep character moments.
This time around, much of the story centers on River Cartwright, played by Jack Lowden. The show takes us through emotional and dangerous twists, including a bombing in downtown London, a tense trip to France, and some heartbreaking deaths.
The Cartwright family’s complicated relationship is at the heart of the story, with River facing both professional and personal challenges.
Alongside River’s story, we meet some new characters who add more complexity to the plot, while returning favorites continue to face difficult moments, especially when the beloved Slough House team faces another painful loss.
This season does more than just continue the story; it focuses on human emotions, sacrifices, and loyalty. With the usual sharpness and tension, Slow Horses shows how its characters respond to danger, betrayal, and the ghosts of their pasts. At the center of all this is River, who grows as both a spy and a man, confronting his troubled family history in a gripping series of events.
River Cartwright Faces Family Betrayal and Emerges Stronger
From the very start of Season 4, it becomes clear that River will have a lot to deal with. River Cartwright has always had a complicated relationship with his family, particularly with his grandfather, David Cartwright (Jonathan Pryce), who was a former British spy himself.
As a former MI5 agent, David has always influenced River’s life choices, for better or worse. In this season, we learn even more about River’s past, which has been shaped by his family’s deep connections to espionage.
But nothing could prepare him for the bombshell that is dropped on him during these episodes: his father, Frank Harkness (Hugo Weaving), is not only alive but also a ruthless criminal mastermind.
Frank Harkness is revealed to be behind the bombing of Westacres, a violent attack that rattles downtown London. This shocking attack shakes up the world of MI5 and everyone connected to it. But even more shocking for River is the discovery that his father is the one responsible for this horrifying crime.
River has spent most of his life believing that his father was dead, but now, he finds himself face-to-face with a man who has not only caused great harm to others but has also personally targeted River’s family.
Frank has made several attempts on David Cartwright’s life, leaving River torn between his duty as a spy and the personal pain of confronting his own father.
This revelation leaves River feeling betrayed, angry, and confused. Frank is not just an ordinary criminal. He is a cold-blooded killer who has committed some of the worst crimes imaginable, including terrorism and murder.
The fact that Frank is River’s father adds layers of emotional complexity to the story. River must now decide how to handle this personal betrayal while continuing to do his job.
Frank is not easy to catch. Throughout the season, Frank tries to escape from both MI5 and the London police. Emma Flyte (Ruth Bradley), Louisa Guy (Rosalind Eleazar), and others are on his trail, but Frank manages to stay one step ahead of them for much of the season. Despite his criminal actions, Frank is incredibly clever, and it’s clear that he is playing a long game.
A Game of Smarts: River Outsmarts His Father
One of the most intense parts of the season comes when River finally gets the chance to confront his father. Despite all the tension and anger between them, Frank underestimates River’s intelligence and skills. River uses something Frank himself taught him to outsmart him, proving that even though Frank may have raised him in part, River is his own person and a highly capable spy.
When Frank is captured and taken in for interrogation, he remains smug and confident. He tells Diana Taverner (Kristin Scott Thomas) that he expects to be released soon.
This arrogance is rooted in the fact that Frank has a secret weapon. He has collected damaging information on MI5’s activities and knows that if this information is made public, it could ruin many high-ranking officials.
During his interrogation, Frank shows no remorse for his actions. Instead, he is calm, cool, and manipulative. He knows that he holds all the cards, and despite Diana’s tough questioning, he continues to play his game. Just when it seems like she might break him, Emma Flyte returns with the news that Frank will indeed be released.
This is because Frank’s fail-safe plan has worked: he has information that can destroy MI5, and this makes him too dangerous to keep in custody. Frank’s ability to manipulate the situation even from behind bars shows just how dangerous and powerful he really is.
The Tragic Loss of Marcus Longridge
While River deals with his struggles, the other members of Slough House also face life-threatening danger. One of the biggest emotional moments in the season is the death of Marcus Longridge (Kadiff Kirwan). In a violent shootout with Patrice (Tom Wozniczka), who is Frank’s right-hand man, Marcus loses his life while defending Slough House and his fellow agents.
Patrice has been sent to kill David Cartwright, and in the process, he storms into Slough House, where the agents have taken shelter. Marcus, along with Shirley Dander (Aimee-Ffion Edwards), Catherine Standish (Saskia Reeves), Roddy Ho (Christopher Chung), and newcomers J.K. Coe (Tom Brooke) and Moira Tregorian (Joanna Scanlan), are caught in the middle of this dangerous situation. Despite being outgunned, Marcus bravely tries to protect everyone, but in the end, he is shot and killed by Patrice.
This loss hits the team hard, especially Shirley, who has always had a close working relationship with Marcus. In the chaos of the shootout, Shirley takes up arms and fights back, despite being deeply shaken by Marcus’s death. Her anger and determination drive her to wound Patrice, but he survives the attack and is about to kill her.
In a tense moment, Jackson Lamb (Gary Oldman) finally arrives and is able to knock Patrice out. But the real surprise comes when J.K. Coe, who has been quiet and mysterious throughout the season, steps up and finishes Patrice off with a shot at close range.
Marcus’s death is a huge blow to the Slough House team, and it also serves as a reminder of the risks that come with their line of work. Even though many people see them as rejects and failures, these agents continue to put their lives on the line for their country.
Jackson Lamb, who is usually cold and indifferent, ensures that Marcus’s family will receive a larger pension, showing a rare moment of care and responsibility for his fallen comrade.
Shirley’s Moment to Shine
Shirley Dander’s character grows even more during this season. After Marcus is killed, she finds herself in the position of the last remaining field agent. Up until this point, Shirley has often been portrayed as reckless and impulsive, but in this moment of crisis, she shows incredible courage. Her actions during the shootout prove that she is capable of handling intense pressure, even when the odds are against her.
Shirley’s development throughout the season shows how much she has grown since she first joined the team. She is no longer just a reckless agent; she is someone who can take control when needed and protect those around her.
Her relationship with the other members of Slough House, especially with Marcus and Roddy, adds emotional depth to her character. Shirley is more than just a fighter; she is a key part of the team, and her role in this season proves her importance.
Moira Tregorian’s Return to MI5
In addition to the intense action, this season also sees the return of Moira Tregorian (Joanna Scanlan), a former MI5 agent. Moira has been out of the game for some time, but by the end of the season, she can use her connections and her knowledge to get her old job back. She blackmails Claude Whelan (James Callis) with information about his affair, ensuring that she can return to MI5.
Moira’s return adds another layer of intrigue to the show, as her character brings a new level of complexity to the already complicated world of British espionage.
Her ability to manipulate those around her and use their secrets to her advantage shows that she is just as dangerous as any of the more obvious villains in the show. Moira is a reminder that in the Slow Horses world, nothing is ever simple, and even those who seem trustworthy can have their own hidden agendas.
The Final Goodbye: River and Jackson Find Common Ground
The emotional core of the season comes to a head in the final scenes. After everything that has happened, River has to make the difficult decision to place his grandfather, David, in an assisted living facility. David’s mind is deteriorating due to dementia, and despite his protests, River knows that this is the best decision for his grandfather’s safety.
David’s pleas for River to keep his promise not to leave him behind are heartbreaking. He repeatedly says, “You promised me,” trying to convince River not to go through with the decision.
But River, torn between his love for his grandfather and his responsibility to ensure David’s well-being, has no choice. This scene is a powerful reminder of the sacrifices that River has had to make, not only as a spy but also as a family member.
After this emotional goodbye, River is understandably shaken. He leaves the facility feeling sad and defeated. But in a surprising twist, Jackson Lamb calls him and invites him to have a drink at a local pub.
This may seem like a simple gesture, but it is a major turning point in the relationship between River and Jackson. For most of the series, Jackson has treated River disdainfully, seeing him as another failed agent. But in this final scene, Jackson shows River a rare moment of respect.
As they sit together at the bar, Jackson hands River some papers to sign, referring to them as an “account of his movements.” This small gesture is significant because it shows that Jackson is finally beginning to see River as a peer, rather than just a member of the Slough House misfits.
The scene ends with the two men sitting side by side, sharing a quiet drink. It is a silent but powerful moment that shows how far River has come throughout the season.
What’s Next for Season 5?
As Season 4 ends, there are still many unanswered questions. Will Frank Harkness return as a villain in Season 5? How will River cope with the fallout of his father’s betrayal and the loss of his grandfather? Will the Slough House team recover from the loss of Marcus? And what new challenges will they face in the future?
While we don’t have all the answers yet, one thing is certain: Slow Horses continues to deliver gripping, emotional, and intense storytelling that keeps viewers on the edge of their seats. Season 5 promises to bring even more drama, danger, and intrigue as the team faces new threats and challenges.
Season 4 of Slow Horses takes the spy thriller to new emotional and action-packed heights. With River Cartwright at the center, this season is deeply personal, focusing on his family’s complex history and the shocking revelation of his father’s betrayal.
The loss of Marcus Longridge in the line of duty reminds us of the high stakes faced by the Slough House team, where loyalty and sacrifice are a daily reality. The intense moments between River and Frank Harkness show how even the closest family bonds can be shattered by greed and ambition.
Shirley Dander’s bravery and growth as an agent, along with Jackson Lamb’s rare moment of respect toward River, are key emotional beats that give this season depth.
The team at Slough House may be labeled as rejects, but their courage and determination prove otherwise. Meanwhile, Moira Tregorian’s return to MI5 adds more intrigue and complexity, setting up future power plays.
As Season 4 closes, many questions remain, especially about the future of Frank Harkness and the dynamics within Slough House. Season 5 will likely show the aftermath of these events while continuing to dig deeper into the lives of its flawed but heroic characters.
With the unique combination of personal drama and high-stakes espionage, Slow Horses remains a must-watch show that keeps viewers eagerly awaiting what comes next.
