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Season 5 of Slow Horses premiered with two episodes on 24 September 2025, with weekly releases amping up the stakes for the Jackson Lamb-led Slough House team. Season 4 ended with a new threat, setting the stage for an action-packed six episodes. With an army of mercenaries at his disposal, Frank Harkness' release from custody can only mean really bad things for the crew.
Created by Will Smith, the spy action drama is known for its shocking twists and turns. So with character deaths that need to be addressed, mysteries that haven't been revealed, and the fate of the Slough House hanging in the balance, there are many questions that season 5 of the Emmy award-winning Slow Horses must tackle. It will be intriguing to see where the show goes from here, since it has already been renewed for two more seasons.
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Disclaimer: All opinions in this article belong solely to the writer. Spoilers for Slow Horses ahead.
Jackson Lamb's origins, River's complicated family dynamics, and other questions that Slow Horses season 5 must tackle
1) What does Shirley's future look like after losing Marcus?
Marcus met an untimely end in Slow Horses season 4, after one of Harkness' assassins accidentally got him instead of David Cartwright. It is a huge blow for the Slough House, especially because of how much lighthearted humor he brought to the dreadful premise. But no one was more upset than his cynical partner, Shirley. They were an inseparable duo whose mutual trust and respect were unshakeable.
However, there was not enough time to explore exactly how this changes her demeanor. What does her grief look like? Episode 1 of season 5 already shows her displaying symptoms of PTSD. She is one of the most volatile characters with a history of cocaine addiction, so would that affect the way she moves forward in pursuit of Harkness? Only time will tell.
2) What is Jackson Lamb's origin story?
There is a lot left unsaid about Gary Oldman's gravitas as Jackson Lamb. After a mysterious past as an MI5 agent, he oddly becomes the head of Slough House. Even if he is overseeing the leftover agents who've messed up, he is very much a part of them, shunned from the mainland. Fans only get a few glimpses of his life during the Cold War and his partner's betrayal as a KGB informant.
Lamb is also an incredibly complex man. His disheveled appearance cloaks the traumas of his past, but he does not let that stop him from being shrewd and stepping up for his team in Slow Horses. What led him to the Slough House? Why is he so respected even if he is not well-liked? Diving into his story would make total sense now that the stakes are higher than ever.
3) What will River do with his family dynamics?
In Slow Horses season 4, River must come to terms with the devastating fact that Frank Harkness, the MI5 agent-turned mercenary and their biggest threat yet, is his biological father. This coincides with digging deeper into his blurry childhood memories with his grandfather, another MI5 agent, and piecing together what led him to be a spy and to the Slough House.
Season 5 must be a moment of becoming for River. He tried his best to bring Harkness down, but the mercenary used his connections to get out of custody. That means River's future is at stake. Who was he meant to be, according to his father and grandfather? Will he go by their plans or go down the road not taken and become who he wants to be?
4) Will the relationship between Slough House and Regent Park change?
A lot of things changed in season 4, so how will the relationship between Slough House and Regent Park change in Slow Horses season 5? There are some unanswered questions about the long-standing rivalry between Lamb and Taverner, and why they meet and debrief so often.
If the Slough House is for the leftovers whom nobody cares about, why is Regent Park so keen to know everything about them? Will there be a power dynamic shift if agents at Slough move back to being MI5 agents after proving themselves? Why is there so much tension between the two entities? Will that play into their hunt for Harkness?
5) What is Coe's history?
The Slough House has a lot of mysterious figures with interesting pasts. The most recent one to join the ranks is J.K. Coe, whose trauma precedes him. However, nothing much is revealed about him in Slow Horses season 4. He is an enigma, quiet and keeping to himself. What is his history? While the book series by Mike Herron digs deeper into his story, the show has yet to get into it.
Without revealing much, Coe's character has become an instant fan favorite. This comes down to Tom Brooke's intense but understated acting. In the season 4 finale, he takes down Marcus' killer, revealing his demeanor. Given this popularity, the show must explore more of his past. Will he play a bigger role in the Slough House operations this season?
6) What is going on with Diana Taverner?
Things have always seemed murky with the Deputy Director of Operations, Diana Taverner. She is nothing if not a scheming and manipulative character, always looking for the right opportunity to pull her power moves. There is a sense that she knows way more than she can let on. So the question is: What is it?
Harkness reveals at the end of Slow Horses season 4 that people at MI5 know about his operations. If he is referring to Diana, there could be much bigger power struggles at play here. What is her plan, and why is she elusive? Her past, motives, and intent would make for a great storyline.
7) Is everyone at Slough House safe this season?
One thing about Slow Horses is that nobody is ever truly safe. That raises the question: Will fans see more casualties in season 5? Marcus' death came out of the blue and rocked the crew at Slough House, but that seemed like just the beginning. With the team getting into the weeds with Harkness, anything is possible.
The season 5 trailer set up techie Roddy Ho's story with his new girlfriend, which changes the tonality of the show. He is more of a conspiracy theorist, and his character brings a lot of comic relief, which might prove interesting in the wake of a new and active threat.
Watch Slow Horses on Apple TV+.
