The Evolution of a Spy: Jack Lowden on River Cartwright’s Descent and Rebirth in ‘Slow Horses’ Season 5
For five seasons, Apple TV+’s critically acclaimed spy thriller Slow Horses has subverted the tropes of the espionage genre. Instead of slick, globe-trotting heroes, we have the "Slow Horses"—a ragtag group of disgraced MI5 agents relegated to Slough House, presided over by the abrasive, flatulent, yet undeniably brilliant Jackson Lamb (Gary Oldman). At the center of this dysfunctional family is River Cartwright, played with sharp-edged vulnerability by Jack Lowden.
As the series moves through its fifth installment and looks toward a sixth, River’s trajectory has shifted from the ambitious, golden-boy recruit to a man haunted by the revelation that his own bloodline is stained by sociopathy.
The Weight of the Past: Unmasking the Harkness Legacy
The narrative arc of Slow Horses underwent a seismic shift in Season 4, which introduced the terrifying reality of River’s heritage. The revelation that his father, Frank Harkness (portrayed with chilling menace by Hugo Weaving), was not only a sociopath but the architect of an international network of assassins has fundamentally altered River’s psyche.
"I think for anybody, that would be quite traumatic," says Jack Lowden, reflecting on the psychological toll the revelation has taken on his character. "The damage carries over into Season 5. His base of operations, Slough House, has become a bit too much for him. When I was filming that season and Season 6, his grandfather is at the forefront of my mind. I feel like that begins to overtake his ambition because he wants to make his grandfather proud. He’s not in the best of head space, and he’s thinner physically. I think nerves-wise, he’s thinner. I don’t think he’s particularly in a happy place or particularly well, so to speak."
This physical and emotional degradation is a deliberate choice by Lowden, who has spent years inhabiting the role. The "thinner" appearance is a manifestation of the relentless pressure River is under, caught between the sins of his father and the failing health of his hero.
Chronology of a Crisis: Why River Lies
The fifth season places River in a precarious position, particularly in the mid-season episode "Circus," where he is seen withholding the truth from Jackson Lamb regarding the death of politician Dennis Gimball. For viewers accustomed to River’s desire to prove his worth, this deception signals a profound shift.
"What I’ve always found interesting about River is his pride," Lowden explains. "I find pride in people incredibly petty, and it pushes people to do stupid things for the sake of how they look or how they come across. He’s trying not to look bad. This season, he’s not in a great head space. I love the fact that, no matter that his personal life is falling apart, at the end of the day, at work, he still doesn’t want to look stupid."
This internal conflict creates a fascinating tension. River is a man trying to maintain the facade of a competent intelligence officer while his internal world is collapsing under the weight of family trauma and professional stagnation.
The Heart of the Show: The Grandfather-Grandson Dynamic
One of the most moving aspects of Slow Horses remains the bond between River and his grandfather, David Cartwright, played by the legendary Jonathan Pryce. The scenes set in the garden, where the two engage in heart-to-hearts, offer a rare moment of stillness in an otherwise chaotic series.
"Jonathan and I talk about that quite a lot," says Lowden. "Losing someone is horrific, and the grief is terrible. But you are watching someone in front of you disappear slowly, with the terrible disease of Alzheimer’s or dementia. I’ve not experienced it yet, but I can imagine it’s horrific. On top of that, his grandfather is his hero. He’s also trying to emulate his grandfather and follow in his footsteps, and to watch him evaporate in front of him is terrible."
Despite the tragedy, Lowden finds a silver lining in these encounters. "In true Slow Horses fashion, David will still give him a little seed of something that will sort of open up the entire thing for him. I took that as a real moment of hope. I think, in the moment, River is very much focused on the problem at hand. But when you get someone who has that condition, and there are these little kernels of hope that they are still who they were—it’s just so moving."
The Art of Heavy Performance: Preparing for the Darkness
How does an actor sustain such a heavy emotional load without letting it bleed into their own life? For Lowden, the key is playfulness.
"I tend to stay away from those moments as much as possible," he reveals. "I try to come at them from as jolly and playful a place as I can, because I think that’s true to what happens in life. When you’re faced with grief, sadness, or tragedy, you’re trying really hard not to give in to the terribleness of the situation. So I tried to do that with these scenes. I don’t spend the night before pushing myself into a certain state. The challenge of just instantly trying to put yourself in that situation and using your imagination—at the end of the day, that’s what I feel makes it fun."
Implications for the Future: A Lingering Presence
By the conclusion of Season 5, River believes he has secured his escape from the purgatory of Slough House. Having executed a series of impressive feats—including the critical rescue of James Callis’s character—he feels he has earned his stripes. Yet, in a move typical of Jackson Lamb’s manipulative brilliance, River remains tethered to the office.
"As far as he’s concerned, he’s pulled off a lot of impressive feats," says Lowden. "He has the chance for a promotion and lays it at the door of what is probably the worst boss in history. River and Lamb are intrinsically linked, but they’re often kept apart, which makes their interactions more special when they do happen. There’s more respect for Lamb now, but I do think we leave River in a more hopeful place than where he was at the beginning of the season. I’m glad about that because, during this season in particular, he’s not exactly a happy bunny."
Reflections on Growth: From Actor to Character
The five-season journey has been as much about Lowden’s growth as an actor as it has been about River’s evolution. "This is the only experience I’ve had doing anything recurring for this long," he notes. "I find it incredibly hard, whenever I do watch the show, to differentiate myself from River because I’m also watching a guy who was 29, I think, when I began. I’m now 36, and the world has been through a lot in that time. Everybody has."
This long-form storytelling has allowed Lowden to chart a unique path. "I think what I’ve enjoyed is seeing myself grow up as an actor as well. It’s why I still act. It’s not necessarily because I want to play all the great characters—though, of course, there are people I want to work with and still haven’t worked with. But I go to work every day because I want to get better at what I do. I can see my progression. I just see a boy who’s sort of eventually becoming a man. Hopefully."
Looking Ahead: Ambitions and Collaborations
As the show looks toward the future, Lowden remains hungry for new challenges. When asked about potential collaborators, he points to the industry’s elite. "Matthew Macfadyen; he’s a benchmark for me. I find his range remarkable. I think he’s phenomenal, and I would desperately love to work with him. Last year, I was very fortunate to work with Martin Freeman. He is another actor that I think has incredible range and has a severely sharp technical ability that I got to see up close night after night."
As Slow Horses continues to peel back the layers of its ensemble cast, the audience is left with a character in River Cartwright who is no longer defined by his need for approval, but by his endurance. He remains a Slow Horse, but as the seasons progress, the lines between "failure" and "necessary asset" continue to blur—perhaps, in the end, that is the greatest victory one can hope for in the world of espionage.
