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Jack Lowden returns as River Cartwright in season 4

Slow Horses season 4 ending explained - what happened to Frank and more

Jackson Lamb and the team live to see another day - mostly

Emmy Griffiths
TV & Film Editor
2 minutes ago
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Slow Horses season four is finally out, and for keen fans of Jackson Lamb and his crew at Slough House, it is already all over thanks to binge-watching the latest six-episode installment! In season four, the gang has to root out a decades-old mystery as old spooks start getting assassinated. But how did it all go down? Warning, major spoilers for season 4... 

What happens in Slow Horses season 4?

Season four kicks off with River's grandfather, David Cartwright, killing a home intruder impersonating River, who was planning to assassinate him. After tracking down the would-be killer's origins, River discovers that an ex-CIA agent by the name of Frank Harkness was running an operation to raise infants into trained assassins, and worked with organisations to quietly and effectively murder their targets.

WATCH: Slow Horses season four trailer

After one of Frank's operatives makes national news by crashing a car bomb into a shopping centre while using the fake identity created by the MI5, Frank's criminal gang takes a hit.

Hugo Weaving has joined the Slow Horses cast© Jack English
Frank was presumably released from custody

 Knowing that he has to eliminate anyone who could trace the fake identity back to him and his operation, he sends men to kill the spooks who worked out a deal with him back in the 1980s - and are in the know about his scheme. 

In this case, David Cartwright arranged for Frank to receive money and weapons in exchange for him returning his daughter Rose, with whom Frank was in a relationship. 

Gary Oldman returns as Jackson Lamb in Slow Horses
Jackson joined River for a drink

For eagle-eyed viewers, this revelation of course means that River's biological father is actually Frank, who attempts to recruit River into his organization. After pursuing his father with MI5, River eventually manages to catch him - and he is arrested. 

Despite Frank landing in custody, he gleefully insists that he will shortly be released. It is revealed by Jackson that Frank has a "failsafe" of compromising information on all of the heads of services, who secretly used his service for MI5 work. 

Will you be watching Slow Horses season 4?© Jack English
Will you be watching Slow Horses season 4?

Jackson explained: "The gist of it is you've got 12 hours to let Harkness go… [or] these letters go up on the web. Harkness has been doing our dirty work for us and our contemporaries for years… You're going to let him go then get some psycho prince off his case."

Although it isn't explicitly shown, it appears that Frank will be released to continue his criminal activity in exchange for his silence. 

Who dies in Slow Horses season 4?

Sadly, poor Marcus Longridge doesn't escape the latest situation unscathed and is shot and killed by one of Harkness' assassins who was sent to murder David, who is being kept safe at Slough House. 

Ready to return to Slough House in Slow Horses season 4?
Marcus was killed

Shirley is deeply tempted to kill Marcus' assassin in retaliation but is talked out of it by the newest, mostly silent member of Slough House, Coe, who offhandedly kills the assassin for her instead. In a rare moment of affection for his team, Jackson insists that Marcus' family is given ten years of full pay as an "active agent increment."

HELLO!'s favourite Apple TV+ shows

Brie Larson as Elizabeth Zott© Apple TV+
Brie Larson stars as Elizabeth Zott in Lessons in Chemistry
  • Bad Sisters - A dark comedy that follows four sisters who set out to free a fifth from an abusive husband. 
  • Hijack - Idris Elba leads the cast as Sam Nelson, a courageous hostage onboard a hijacked commercial plane on a seven-hour flight from Dubai to London.
  • Slow Horses - Star-studded spy thriller that follows a group of misfit intelligence agents who have been banished to the dumping ground department of MI5 after making career-ending mistakes. 
Gary Oldman as Jackson Lamb in Slow Horses
Gary Oldman as Jackson Lamb in Slow Horses
  • Lessons in Chemistry - Brie Larson stars in this adaptation of Bonnie Garmus's bestselling novel. It follows chemistry genius Elizabeth Zott, whose dreams of becoming a scientist are stunted by 1950s sexism. 
  • The Buccaneers - A frothy period drama that sees five young, rich American girls journey from New York to 1870s London, where they enter High Society in a bid to bag themselves an aristocrat.
Did you spot Mia in The Buccaneers?
Mia Threapleton in The Buccaneers
  • Ted Lasso - Jason Sudeikis plays a hapless American coach who comes to the UK to manage struggling football team, AFC Richmond. 
  • The Morning Show - Jennifer Aniston and Reese Witherspoon star in the drama, which examines the culture behind a network news show. After her co-star is accused of sexual misconduct, anchor Alex Levy is handed the reins to The Morning Show. 
  • Silo - A dystopian murder mystery thriller in which the last of humanity live underground in a giant silo and are forced to follow strict rules they believe are in place to protect them. 
Reese Witherspoon in The Morning Show© Apple TV+
Reese Witherspoon in The Morning Show

What happens to Moira Tregorian?

Slough House briefly welcomes an incredibly efficient, thoughtful secretary named Moira. Since she is clearly excellent at her job, it is obvious to Jackson that she has been sent to Slough House because she annoyed someone - with that someone turning out to be the new First Chair, Claude Whelan.

Joanna Scanlan has joined Slow Horses for season 4© Jack English
Moira got her old job back

With help from the insufferable IT genius Roddy Ho, they discover that Moira inadvertently worked out that Whelan had been curb crawling under the moniker of 'Galahad.' Meeting him to share the information, Moira negotiates a four-day week and a pay rise, returning to the main building at MI5. Good for her!

Slow Horses is back for season 4
Whelan managed to keep his job as First Chair - just about

What Happens to David Cartwright?

Things take a sad turn for David, as despite surviving several assassination attempts, he is unable to look after himself anymore. River is forced to put him in a care home for his own safety and is left guilt-ridden as David begs him not to leave him. He ultimately cheers up when Jackson calls him to the pub and begrudgingly suggests that he may stick around for a drink, bizarrely becoming the best father figure in River's life at that point. Which isn't saying much!

Jonathan Pryce stars in Slow Horses season 4
David was put in a care home by River

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