InSlow Horsesseason 4, episode 5, “Grave Danger,” some of the show’s lingering mysteries are finally unraveled. While the previous outing,Slow Horsesseason 4, episode 4, all but confirmed thatRiver Cartwright’s (Jack Lowden) mother was one of the women who lived at Les Arbres, the fifth episode doesn’t skirt around the big reveal. At the end of episode 4, River snuck into his grandfather’s house only to be apprehended by Emma Flyte (Ruth Bradley), the new (and already disillusioned) Head of the Dogs. Meanwhile, Jackson Lamb (Gary Oldman) made it his mission to locate David Cartwright (Jonathan Pryce).
With Flyte’s Dogs hot on the elder Cartwright’s heels, Lamb employed the help of formerSlough House agentCatherine Standish (Saskia Reeves) and Sam Chapman, David’s ex-bagman. While Standish and Lamb managed to flee the scene with David, Chapman went off on his own to retrieve his flight fund. Before he could flee the country, however, Chapman was attacked and killed by Frank Harkness' (Hugo Weaving) assassin, Patrice. With both Frank and MI5 gunning for the Cartwrights,Slough House still has a few cards left as SlowHorsesraces toward its finale.
8Molly Doran Is Visited By Frank Harkness
Frank Reveals He Used The “Mitch Philpott” Alias To Get Info Out of Molly
In the opening moments of episode 5, Molly Doran, the Park’s head of records, receives a surprise visit from Frank Harkness. The former head of the Les Arbres compound and an assassin-for-hire, Frank is under pressure from his boss — an unnamed foreign dignitary — to make up for the WestAcres bombing incident. Evidently, the bombing was Frank’s bright idea. Although he intended to take out a single target,Frank thought the bombing would throw MI5 off the scent of the real victim. Unfortunately for Frank, the discovery of the Robert Winters cold body soured that idea.
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Knowing that he must eliminate anyone who can connect him to WestAcres and the cold bodies — ready-made identities that MI5 made back in the Cold War era — Frank’s kill list includes Chapman and David Cartwright. After failing to apprehend either Cartwright in episode 4, Frank shows up at Molly’s flat to try and track his remaining targets.The assassin also reveals that he impersonated Mitch Philpott, a former MI5 operative, to squeeze Molly for David and Chapman’s information. With her life on the line, Molly acquiesces to Frank’s demands. Clearly, she feels guilty about the whole ordeal.
7River Shows Flyte What He Recovered From Les Arbres
Flyte Fails To Tell Taverner The Whole Truth & Gives The Photo To Giti & Whelan
In the previous episode, River learns more about his connection toFrank Harkness’Slow Horsesplanat Les Arbres after consulting his mother’s old drawings. However, his life-altering discoveries are cut short when Flyte and her Dogs break into David’s house to apprehend River. Although River manages to outsmart the Dogs, Flyte catches and cuffs him. On the way to the car, River says he’ll talk if he’s allowed to see his grandfather.The Slough House agent also wants Flyte’s word that David will be okay; although he might not know his family’s full Les Arbres connection, River senses the danger.
The finale ofSlow Horsesseason 4 airs on July 29, 2025.
Flyte is frustrated that River is making demands, but she isn’t really in a great position to barter either. Eventually, River decides to show her the photograph he recovered from Les Arbres, which depicts Frank and his soldiers — Patrice, Bertrand, and the man who used the Robert Winters alias. Flyte recognizes two of the men in the photo, connecting Winters to the WestAcres bombing. Although Flyte calls Diana Taverner (Kristin Scott Thomas) to tell her that she has apprehended River,the Head of the Dogs leaves out the photograph.
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River calls Flyte out for her distrust, though he agrees that Taverner operates on her own whims. Flyte, who formerly worked for the police, is frustrated that everyone at MI5 also has their own agendas. WhileRiver resents being lumped in with the likes of Taverner or Lamb, he understands where Flyte is coming from.
6River’s Mother Calls Louisa Guy
While Louisa Guy (Rosalind Eleazar), Shirley Dander (Aimee-Ffion Edwards), and Marcus Longridge (Kadiff Kirwan) are on a bus back to Slough House, the former receives an unexpected call. When Louisa answers, River’s mother is on the line. Evidently, Louisa had called River’s mother when she thought River had died in David’s bathroom. Louisa clarifies that someone who looked like River was killed and that her son is missing in action in the field. When Louisa starts to mention David, River’s mother dismisses her. David has not spoken to his daughter in years;Louisa is shocked by the Cartwrights' estrangement.
Someone who went by the name “Galahad” was involved in a scandal with sex workers — and, as Roddy discovers, is the reason that Moira was sent to Slough House.
At Slough House, Moira Tregorian (Joanna Scanlan), one of the Park’s former Queens of the Database who was banished to MI5’s purgatory, asks Roddy Ho (Christopher Chung) for his help identifying a MET ID. Someone who went by the name “Galahad” was involved in a scandal with sex workers — and, as Roddy discovers, is the reason that Moira was sent to Slough House. After some sleuthing,Roddy reveals that Galahad is none other than First Desk Claude Whelan(James Callis). Afterward, the other Slough House agents arrive and, led by Louisa, the group tries to formulate their next steps.
5Whelan Changes His Position On The Cold Bodies
First Desk Agrees With Taverner About Needing To Bury The Truth
InSlow Horsesseason 4, episode 3,Taverner revealed to Whelan that Robert Winters was one of MI5’s cold bodies— ready-made identities that were made for operatives during the Cold War. Somehow, the assassins responsible for the WestAcres bombing and the attempted murder of David Cartwright got hold of these cold bodies' passports. If word of this massive misstep leaked to the public, MI5 would be in hot water. Taverner, who has already taken the first steps to cover up the agency’s connection to Winters, tells Whelan it is the best course of action.
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At first, Whelan is adamantly opposed to Taverner’s tactics. The new First Desk assigns Giti, a determined young agent, to collate the cold bodies. In episode 5, Whelan presents Giti’s findings to Taverner, illustrating thatthe MI5 IDs have been used over the course of several decades by a death squadof sorts. Of course, this is Frank Harkness' team of assassins, who were born and raised in Les Arbres. Whelan admits that the best thing they can do is seal the truth away in a slab of concrete, though he fears Giti might turn into a whistleblower.
4Jackson Lamb Interrogates David Cartwright About Frank Harkness
Realizing that David Cartwright is on the assassins' kill list because the former head of MI5 knows who’s behind the WestAcres bombing, Lamb decides to interrogate David for more information. Although Standish is opposed to Lamb’s methods, the head of Slough House forges on. Lamb confuses David into admitting the truth. Throughout all ofSlow Horsesseason 4, David has grappled with his worsening dementia. When Lamb brutally convinces him that River is dead,David admits that he did it all “for her.“When Standish asks if he means his late wife, Rose, David reveals he’s talking about their daughter.
…this “deniable assassination squad” would be raised by Frank from birth as child soldiers.
David explains that his daughter, River’s mother, was taken by the man in charge of Les Arbres. When Standish presses David for a name, he reveals what the audience already knows: the man at the center of the conspiracy is Frank Harkness. According to David, Frank is an ex-special forces agent and ex-CIA operative. In building the Les Arbres compound,Frank hoped to create a squad of untraceable assassins for hire. As David puts it, this “deniable assassination squad” would be raised by Frank from birth as child soldiers.
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In order to get his daughter back, David traded Frank the cold body passports. David also furnished Les Arbres with weaponry and money. This was the drop that Chapman made all those years ago on David’s behalf, though he never knew who the woman was that he was rescuing from Frank. To make matters more disturbing,David insinuates that his daughter actually wanted to be with Frank.
3Frank Lets Molly Live & Leaves Letters Behind
Patrice & Frank Finish Tracking Flyte & River
In a surprising turn of events, Molly lives to seeSlow Horsesseason 4’s finale. Although Frank seems poised to kill her for most of the episode, he leaves without firing his weapon at her. Before Frank departs, Patrice, the only remaining Les Arbres soldier, shows up. Patrice confirms that he tortured and killed Chapman for information. In the end,David’s former bagman didn’t give up any useful information, though Patrice did take his phone. Frank informs Patrice that he was outsmarted by MI5’s rejects — Jackson Lamb and other Slough House operatives. Ashamed, Patrice says he should be punished.
It seems Frank wants Molly alive so that she can deliver the messages.
However, Frank has just a few hours left to complete the kill list for his boss. Instead of punishing Patrice,Frank hugs his son and tells him that if only one of his children could be left alive, he’d always have chosen Patrice. Empowered by his father’s words, Patrice leaves to apprehend River. Afterward, Frank threatens Molly but doesn’t shoot her. In Frank’s wake, Molly discovers a series of letters left on her desk. Each of the letters is addressed to someone at MI5, including Claude Whelan. It seems Frank wants Molly alive so that she can deliver the messages.
2Giti Identifies The Men In The Les Arbres Photo
Slough House Races To Identify Patrice & Protect David
In the build-up toSlow Horses' season finale, both MI5 and Slough House race toward similar conclusions. Using Moira’s advanced access to MI5’s databases, Slough House is able to find footage of Patrice. It remains to be seen how positively identifying the seemingly unkillable assassin will help, but, clearly, the so-called slow horses are trying their best. Jackson and Louisa hop on the phone to discuss next steps.Lamb tells Louisa that Standish will be driving David to Slough Housefor safe keeping, while he goes to find Chapman — or what’s left of the former bagman.
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Meanwhile, at the Park, Whelan and Taverner speak with Giti, who has been hard at work identifying the men in the Les Arbres photograph. At the beginning of the episode, Flyte sends the photograph to Giti and Whelan, completely avoiding Taverner. When Giti bursts into the office and mentions the photo, Taverner is taken off guard. Recognizing the WestAcres bomber and David’s would-be assassin, Taverner asks Giti for the names of the other men. Now,both MI5 and Slough House know Frank Harkness' nameand, by extension, his connection to MI5’s cold bodies.
1Patrice Takes River Captive
Flyte Is Knocked Out & The Dogs Are Killed
While most of the main players inSlow Horses' cast of charactersare removed from the action, River and Flyte find themselves at the center of a shootout in the episode’s closing moments.Patrice has tracked the Dogs' carand bursts onto the scene, guns blazing. River is still handcuffed to the door inside of Flyte’s car, leaving him in a pretty vulnerable position. After Patrice takes out the Dogs, Flyte leaps onto the street and fires a few shots at Patrice, who’s busy breaking through River’s car window. Ultimately, Patrice is able to knock Flyte unconscious.
…it’s possible that the Slough House agent was left alive so that he could chat with his apparent biological father.
A terrified River tries his best to twist away from Patrice, but, because of the cuffs, he’s pretty much unable to defend himself. “Hold still,” Patrice mutters — and thenPatrice shoots River free of his handcuffs. It’s a somewhat surprising development given the fact that Patrice was willing to kill just about anyone. Given River’s connection with Frank, it’s possible that the Slough House agent was left alive so that he could chat with his apparent biological father. Needless to say,Slow Horsesseason 4’s penultimate episode sets up a thrilling finale.
Slow Horses
Slow Horses follows a dysfunctional team of MI5 agents led by the notorious Jackson Lamb. Set against the backdrop of the espionage world, the agents must navigate complex operations and defend England from sinister forces, all while dealing with internal struggles and their abrasive boss.
