Spoilers are ahead for Slow Horses season 4, episode 4, “Returns.”
Slow Horsesseason 4, episode 4, “Returns,” reveals a lot more about Frank Harkness (Hugo Weaving) and the mysterious Les Arbres compound. As seen inSlow Horsesseason 4, episode 2,River Cartwright’s (Jack Lowden) investigation into why his doppelgänger was sent to assassinate his grandfather, David Cartwright (Jonathan Pryce), takes him to Lavande. A small town in France, Lavande is home to an abandoned compound, which River later learns is called Les Arbres. Meanwhile, back in London, Jackson Lamb (Gary Oldman) and the rest ofSlough House’s agentstry to cover for River, who effectively faked his own death.
The blood test results have tipped both Diana Taverner (Kristin Scott Thomas), MI5’s Second Desk, and Emma Flyte (Ruth Bradley), the new Head of the Dogs, off about River’s plan. As the pair work to track down the Cartwright men, Taverner uncovers another insidious thread. InSlow Horsesseason 4, episode 3, it’s revealed that the bombing of WestAcres shopping center is tied to MI5 and Les Arbres.The bomber was carrying a cold body passport — one of MI5’s ready-make IDs from the Cold War. In episode 4, the truth aboutRiver and Frank’s connectionfinally comes out.
9Frank Harkness Is Working For Someone Else
The Contract Killer Is Tasked With Killing Anyone Connected To WestAcres By Midnight
Slow Horses' fourth episode opens by revealing a little bit more about Frank Harkness, the mysterious man at the center of the WestAcres bombing and whatever happened at Les Arbres. Previously, viewers only saw glimpses of Frank. From afar,Frank instructs one of his assassins to track down and kill both David and the former MI5 head’s bagman, “Bad Sam” Chapman(Sean Gilder). Later, he also tries to strangle River in Les Arbres before burning down the place and, with it, any evidence of his past activities. Thankfully, Frank gets more than a few lines of dialogue in episode 4.
New episodes ofSlow Horsesseason 4 premiere on Wednesdays on Apple TV+ through August 11, 2025.
After subjecting himself to a thorough pat down, Frank Harkness meets with a foreign official.Slow Horsesis vague on the details of whom the man is, but it’s clear he’s a foreign dignitary who wants to quietly cause trouble for the UK.The WestAcres bombing was Frank’s clever way of killing a target without attracting suspicion.Of course, it attracteda lotof suspicion, so the man who hired Frank is incredibly frustrated. Wanting to tie up loose ends, he threatens to kill Frank on the spot.
Frank is able to talk his way out of being tortured and killed on the floor of a hotel room. He explains that he can’t have his involvement compromised either; clearly, he has some kind of past connection to MI5.The dignitary gives Frank and his assassin until midnight to tie up any loose ends.That means Frank plans to kill both David and Chapman within the next few hours.
8Taverner Shows Up At Slough House To Speak With Jackson Lamb
Lamb Tells Taverner About The Cartwrights & Questions Flyte’s Competency
Realizing that Taverner is waiting outside Slough House for a chat, Jackson Lamb decides to leave Chapman and the rest of his crew in the stolen taxi cab while he deals with Second Desk. Standing in the rain, the pair discuss the fact that Lamb outright lied to Flyte. Lamb has no need to hide the truth. Instead, he explains that he was protecting River and doesn’t care much about Flyte’s tactics or opinions.Taverner is clearly upset with Flyte’s lack of progress. Taverner’s frustration is hardly surprising; after all, it’s always Lamb and River who cause trouble.
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While Taverner probably didn’t expect Lamb to reveal David Cartwright’s whereabouts, she still angles for some information. Lamb insists that he told Flyte the truth on that one. David had been at Catherine Standish’s (Saskia Reeves) flat. The delicate dance between the two MI5 agents yields very little results for either party. During the alleyway chat,Lamb assumes Standish still has custody of David Cartwright. At the end of episode 3, David gave Standish the slip to speak with First Desk himself. Realizing that Lamb is getting her nowhere fast, Taverner leaves.
7Standish Returns To Slough House To Track Down David Cartwright
David Is Seemingly Headed To The Park To Speak With First Desk
While Lamb is out in the rain chatting with Taverner, Standish hangs around her old stopping grounds. Standish’s replacement, Moira Tregorian (Joanna Scanlan), offers her some tea. At first,Standish seems put off with the way Moira is running Slough House, but is surprised to hear that Moria can’t wait to get promoted back to the Park. It’s possible Standish’s MI5 days aren’t officially over. Judging by her involvement in the Cartwright situation, it seems Standish doesn’t know how to walk away. However, things don’t go well when Lamb and Chapman return, expecting to see David in Slough House.
It’s possible Standish’s MI5 days aren’t officially over. Judging by her involvement in the Cartwright situation, it seems Standish doesn’t know how to walk away.
Standish explains that she moved David rather hastily into her neighbor’s flat while Flyte went to search her apartment. Ever-determined to find First Desk and explain what happened, David slips away into the rain. Standish explains that Louisa Guy (Rosalind Eleazar) is stationed outside the Park to intercept David when he arrives, butLamb, Chapman, and Standish all come to the realization that David, who’s navigating dementia, probably went to MI5’s former headquarters.The Park that David once worked in is now a hotel. Before the trio leave, Chapman explains what he knows about Lavande.
6Chapman Explains That He Delivered Cold Bodies, Weapons & Money To Les Arbres
In Lavande, Chapman Extracted A Young Woman In Return For The Supplies
Decades earlier, David Cartwright tasked Chapman with making a drop at Les Arbres, the compound on the outskirts of Lavande. Chapman wasn’t told much about what he was doing and, in typical MI5 fashion, he didn’t ask many questions either. Still, he recounts in great detail what happened that day. After arriving in France, Chapman drove an MI5-supplied car to the compound. When he pulled up, a bunch of men came out of the house to search and strip the vehicle.Much to Chapman’s dismay, the car was full of weapons, ammunition, passports, and money.
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In the flashback, Les Arbres is only a slightly more lively place. In addition to the armed men who flank their leader, there are some women and children scattered about the compound. What Chapman sees echoes what River discovered in episode 2: Les Arbres seems to be home to a syndicate that’s raising child soldiers. In exchange for MI5’s cold-body passports and weapons,the men of Les Arbres surrender a young woman to Chapman. According to David’s former bagman, the woman said nothing and eventually gave him the slip at a petrol station.
5Taverner Threatens To Fire Flyte
Flyte Is Tasked With Finding David Cartwright Before Jackson Lamb
Back at the real Park, Taverner calls Flyte into her office. In her typically cold manner, Taverner berates Flyte for not only her lack of progress but her insistence on keeping secrets. After Lamb identified the body of River’s doppelgänger as Agent Cartwright himself, Taverner looked into the results of the blood examination. Much like Flyte,Taverner realized Lamb had lied to them and that River was alive and well.Taverner asks Flyte why she withheld that information instead of reporting it to Second Desk. Unfortunately, Flyte’s excuses are pretty weak.
To make up for what’s happened, Flyte is tasked with locating David Cartwright before Lamb.
Flyte, the very newly minted Head of the Dogs, insists that she wanted to catch River or David before coming to Taverner with the news of the blood examination. Essentially, Flyte didn’t want to bombard her superior with bad or lackluster news. Taverner assures Flyte that communication is key. In fact,poor communication is precisely why Taverner didn’t gel with the former Head of the Dogs. While Flyte agrees to do better, Taverner threatens to fire Flyte if she makes another blunder. To make up for what’s happened, Flyte is tasked with locating David Cartwright before Lamb.
The New First Desk Doesn’t Want To Sweep MI5’s Sins Under The Rug
After the Robert Winters incident, Claude Whelan (James Callis) isn’t taking any chances with Taverner. Previously, Taverner blackmailed Whelan, the new First Desk, when she discovered that the WestAcres bomber used one of MI5’s Cold War-era ready-made passports. WhileGiti, a younger agent working at the Park, discovered Winters' connection to MI5, Taverner took matters into her own hands and scrubbed any record of the name. Afterward, she informed Whelan of what happened, insisting a cover-up was needed to shield MI5 from more damaging reports. Whelan has a much different perspective on the matter.
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In episode 3, Whelan approaches Giti with a new assignment. The First Desk tasks the sharp-witted agent with searching for more ready-made identities and connections. Of course, the other passport that’s come into play is the one River found on the body of Betrand, his doppelgänger and David’s would-be assassin. That ID belonged to a cold body called Adam Lockhead. In episode 4,Whelan and Giti discover the Adam Lockhead cold body and call Taverner out for her cover-up. First and Second Desk still don’t see eye-to-eye, with Whelan insisting MI5 come forward publicly with the information.
3Standish & Chapman Find David
Meanwhile, Flyte Tries To Apprehend River At The Train Station
While Lamb loiters in the getaway cab, Standish and Chapman race inside the hotel to locate David Cartwright before Flyte’s men have the chance. Chapman instructs Standish to cause a distraction while he works to peel David away from the hotel lobby. Although David seems to recognize his former bagman, he doesn’t want to leave the Park.Chapman, on the other hand, doesn’t want his connection to Les Arbres getting back to MI5. After securing David, Chapman wants to leave the country. As the Flyte’s men pull up, Standish races to find a fire alarm and pulls it.
…MI5 gets a ping on Lockhead’s passport, which means River is on his way back to London.
In the chaos of hotel guests streaming outside, Chapman is able to sneak David out of the building and into Lamb’s cab. Meanwhile, MI5 gets a ping on Lockhead’s passport, which means River is on his way back to London.Flyte decides to apprehend River herself and takes a group to the train station. River catches sight of Flyte and her men, which prompts an action-packed chase through the station and onto the London Underground. Frank Harkness, meanwhile, had also planned to intercept River. Instead, he watches the chase unfold. Ultimately, Flyte fails to catch River Cartwright.
2Chapman Leaves To Pick Up His Flight Fund
Frank’s Assassin Tortures Chapman For Information
After ensuring that David Cartwright is safely in the cab, Chapman leaves Standish and Lamb to deal with the mess. Terrified of what could happen to him if David speaks out or his mission to Les Arbres is uncovered, Chapman returns to his office. As he tells Lamb, he’s just stopping by to pick up his flight fund. Evidently,hardened MI5 operatives like Chapman all have some cash lying around just in case things go south. With both MI5 and Harkness on his tail, Chapman knows that it’s time to disappear. Before he leaves, Chapman tosses back a drink.
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Once he’s secured the flight fund from a loose ceiling tile, Chapman hears something strange outside. Gun drawn, he investigates the fire escape when Harkness' assassin comes bursting through the window. According to an earlier conversation, Chapman is one of the targets the assassin must take out before midnight if he hopes to save Harkness' skin (and his own). Instead of outright killing Chapman, the assassin tortures and beats him. Since David Cartwright is the assassin’s other target,it’s possible Frank’s man wants to break Chapman and glean some information before killing him.
1River Returns Home & Discovers His Connection To Les Arbres
Flyte Finally Apprehends River In David Cartwright’s House
Once he’s successfully evaded Flyte and her team, River races to his grandfather’s house. Normally, that would be a massive misstep, but River is on a mission. While in Lavande, he met Bertrand’s mother, who explained thatFrank fathered all the children at Les Arbres with the women he abducted. In the compound, River had come across a striking mural and photographed it for evidence. Although Bertrand’s mother hadn’t drawn the mural, she knew the woman who had. Inside David’s house, River finds a box of mementos and digs through it until he uncovers a few drawings.
While River doesn’t say anything, it’s clear that he believes his mother was one of the women held at Les Arbres.
After comparing the drawings in the box to the mural at Les Arbres, the connection feels pretty undeniable. While River doesn’t say anything, it’s clear that he believes his mother was one of the women held at Les Arbres. So far,Slow Horsesseason 4 has really hammered home the fact that David raised River. If River’s mother was held at the French compound,it would explain why David traded so many weapons and passports to ensure a young woman’s safe passagehome.Before that can be confirmed, the episode ends with Flyte apprehending River.
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.
