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