The episode "Returns," Season 4 Episode 4 of Slow Horses, begins with Chapman realizing why assassins are targeting him: he was involved in a covert operation connected to Les Arbres, a secretive compound. Chapman knows he has done something wrong but refuses to reveal details while in the car. He is aware that entering the Park (MI5 headquarters) may be a one-way trip for him, implying grave danger.

Meanwhile, Frank Harkness arrives to meet his superior, who angrily reprimands him for botching the hit at Westacres. Frank was supposed to make the assassination look like an accident, but the resulting spectacle has exposed their operation. Frank faces execution, paralyzed and about to be carved up, but he narrowly escapes death by revealing that some people, including David Cartwright and Chapman, know about the operation. This information spares him and allows him to continue his mission.

Frank then meets with his son, who updates him on the severity of the situation following the events of the previous episode. Frank warns that failure to complete their mission will result in death for them all. He expresses confidence that River Cartwright will return, noting that Bertrand's passport is active. Frank advises his protégé to anticipate where a spook would go when under threat, urging him to resume the pursuit with this strategic mindset.

Back in London, David Cartwright is now in the custody of Slough House, thanks to the efforts of Sam and Standish. David's dementia complicates matters, making him unpredictable and raising questions about how much he remembers about MI5's dark past. David decides to leave Katherine Standish's protection and head to MI5's former headquarters, now a luxury hotel, which sets up one of the episode's most intense sequences.

Chapman and Standish rush to retrieve David from the hotel. Standish pulls the fire alarm to create a distraction, adding chaos to the already precarious situation. Their quick thinking and resourcefulness allow them to barely get David to safety. However, Chapman's loyalty to David proves fatal as he is caught by assassins. The episode ends with Chapman's fate uncertain but grim, highlighting the high stakes and danger surrounding the characters.

The episode also reveals more about Frank Harkness and the Les Arbres compound. It is disclosed that 30 years ago, David Cartwright orchestrated an off-the-books operation involving a Volvo Estate filled with cash, guns, explosives, and MI5-issued fake IDs, which he handed over to a young Frank Harkness at Les Arbres. This operation was to "buy a girl," who was part of Harkness's harem and was traded like chattel. This dark past connection explains why the assassins are targeting David and those linked to Les Arbres.

Throughout the episode, tensions rise as MI5's Second Desk head Diana Taverner and Emma Flyte, the new Head of the Dogs, track down the Cartwright men. They are tipped off by blood test results about River's plan and the connection to the WestAcres bombing, which involved a cold body passport from MI5's Cold War era. The episode sets up a midnight deadline that pressures Frank and his team to eliminate remaining witnesses, including David and Chapman, escalating the urgency and danger.

River Cartwright returns to London by the end of the episode, setting the stage for a reunion with Slough House in the next episode. His return is highly anticipated as the team's camaraderie and bickering are central to the series' dynamic.

In summary, "Returns" unfolds with Chapman's realization of his peril, Frank's narrow escape from execution, the rescue and protection of David Cartwright amid his dementia, and the revelation of a decades-old MI5 operation tied to Les Arbres. The episode ends with Chapman's capture and River's return to London, heightening the stakes for the concluding episodes of the season.

The episode "Returns," Season 4 Episode 4 of Slow Horses, ends with Frank Harkness narrowly escaping execution by revealing that others, including David Cartwright and Sam Chapman, know about the conspiracy tied to Les Arbres. River Cartwright returns to London after investigating the Les Arbres compound in France, ready to rejoin Slough House. Meanwhile, Sam Chapman is in grave danger, pursued by assassins due to his involvement in the Les Arbres operation. The episode closes with mounting tension as the characters prepare for the next phase of their dangerous mission.

The episode begins with Sam Chapman realizing why assassins are after him: his involvement in a covert operation linked to the Les Arbres compound. He is aware that entering the Park--a safe house or meeting place--may be a one-way trip, indicating the high stakes and danger he faces.

Meanwhile, Frank Harkness arrives to meet his superior, who harshly reprimands him for botching the assassination attempt at Westacres. Frank was supposed to make the hit look like an accident, but the public spectacle has drawn unwanted attention. Frank faces imminent execution, paralyzed and vulnerable, but he manages to save himself by revealing that others, specifically David Cartwright and Sam Chapman, are aware of the conspiracy. This revelation spares his life and allows him to continue his mission.

Frank then meets with his son, who updates him on the severity of the situation following the events of the previous episode. Frank warns that failure to resolve the crisis will result in death for them all. Despite the danger, Frank remains confident that River Cartwright will return, noting that Bertrand's passport is active, suggesting movement. He encourages his protégé to anticipate the enemy's moves by thinking like a spook who is being hunted.

River Cartwright returns from France, having uncovered much about the Les Arbres compound and its connection to the London bombings and MI5's darker secrets. He finds the situation in London more complicated than expected, with new threats emerging. River is poised to reunite with Slough House, setting the stage for the team to come together again.

The episode closes with Sam Chapman in dire straits, pursued by assassins who are closing in on him. His fate appears grim, with the implication that unless rescued, he will be killed. The tension is palpable as the episode sets up the final confrontations, emphasizing the dangerous stakes for all involved.

In summary, the main characters' fates at the episode's end are:

• Frank Harkness: Survives an execution attempt by revealing critical information; continues his mission with urgency.
• River Cartwright: Returns to London, ready to rejoin Slough House and continue investigating.
• Sam Chapman: In grave danger, pursued by assassins, with his survival uncertain.
• David Cartwright: Remains a key figure whose knowledge threatens the conspirators.

The episode's ending underscores the escalating danger and the tightening noose around those connected to Les Arbres, setting up a tense and action-packed continuation.

The episode "Returns," Season 4 Episode 4 of Slow Horses (2024), does not have a traditional post-credit scene. The final moments of the episode and the season focus on a significant, emotionally charged scene between River Cartwright and Jackson Lamb. After River places his grandfather David in an assisted living facility, he meets Jackson at a local pub. In this scene, Jackson shows River a rare sign of respect by handing him papers to sign--an "account of his movements"--and they sit side-by-side sharing a whiskey as the screen fades to black and the credits roll. This moment is the closing scene, with no additional post-credit content following it.

Thus, the episode ends on this poignant note without any extra scene after the credits.

The Les Arbres compound is revealed as a key location tied to Frank Harkness and a past MI5 operation involving illicit activities, including the exchange of a young woman for weapons and fake IDs. It is central to understanding why assassins are targeting David Cartwright and others connected to this operation.

Assassins are after David Cartwright and Sam Chapman because they hold dangerous knowledge about a covert operation linked to Les Arbres and the WestAcres bombing. Their involvement in this off-the-books MI5 operation makes them liabilities to those trying to cover up the truth.

Frank Harkness is shown to be the mastermind behind the London bombings and the assassination attempts. He runs a tight operation and is under pressure from his employer to eliminate anyone who can tie him to WestAcres, including David and Chapman. His past dealings at Les Arbres and his ruthless methods are further exposed.

River returns from France after investigating Les Arbres and understanding its connection to the attacks. His return to London sets up a reunion with Slough House and intensifies the pursuit of the truth behind the bombings and assassination attempts, adding emotional and operational urgency to the plot.

It is revealed that Sam Chapman once worked as David Cartwright's bodyguard and was involved in a secretive operation decades ago. Their shared history includes a dangerous mission involving Les Arbres, which, if exposed, would have severe consequences for both, explaining why they are now targets.

The episode "Returns" (Season 4, Episode 4) of Slow Horses is rated TV-MA, indicating it is intended for mature audiences and is not family friendly for children or sensitive viewers.

Potentially objectionable or upsetting content includes:

• Strong violence and scenes involving physical danger or threats, including kidnapping and assassination attempts.
• Strong language typical of a gritty espionage thriller.
• Themes of espionage, betrayal, and covert operations that involve morally complex and dark subject matter.
• Some scenes may involve intense suspense and psychological tension, including characters being tied up or in perilous situations.
• References to trafficking or exploitation implied in backstory elements, which may be disturbing.

Overall, the episode contains mature themes, violence, and language that make it unsuitable for children and potentially upsetting for sensitive viewers.