‘Slow Horses’ Season 4 Ending Explained: Unpacking Those Frank Harkness Twists, And Is [SPOILER] Really Dead?

Apple TV+ ‘s Emmy-winning spy drama Slow Horses ended another suspenseful, whip-smart season with several bangs, one of which tragically took the life of a beloved Slough House fixture.

Based on Spook Street , the fourth installment in Mick Herron’s book series, Slow Horses Season 4 followed delightful curmudgeon Jackson Lamb (Gary Oldman) and his trusty group of MI5 misfits River Cartwright (Jack Lowden), Louisa Guy (Rosalind Eleazar), Roddy Ho (Christopher Chung), Shirley Dander (Aimee-Ffion Edwards), Catherine Standish (Saskia Reeves), Marcus Longridge (Kadiff Kirwan), and new addition J.K. Coe (Tom Brooke) as they raced to investigate a bombing, a threat to David Cartwright’s (Jonathan Pryce) life, and a mysterious new adversary named Frank Harkness (Hugo Weaving).

In true Slow Horses fashion, the Season 4 finale, “Hello Goodbye,” featured fierce conflicts, explosive answers, and flying bullets. So what happened to River after Patrice (Tom Wozniczka) tossed him in a trunk during Season 4’s penultimate episode? Did Frank Harkness get away with all of his crimes? And which one of Slough House’s finest died in the Season 4 finale? We’ve got answers.

Looking for a Slow Horses Season 4 finale recap? Decider’s Slow Horses Season 4 Ending Explained article has you covered.

Following the final action-packed minutes of Season 4’s penultimate episode, “Grave Danger,” which featured Harkness’ assassin son Patrice attacking Emma Flyte’s (Ruth Bradley) motorcade, knocking her unconscious, and shoving River in the trunk of a commandeered car, the finale picked up right where we left off. Flyte woke up, realized River was missing, and checked in with Diana, confirming that the man who took River was in the photo found in France.

In response to the attack on the Dogs, First Fool Claude Whelan (James Callis) — who continues to have no idea what he’s doing — recklessly issued a shoot to kill order on River despite Diana’s (Kristin Scott Thomas) protests. Meanwhile, River — unaware that his own were out to end him, again — was fiddling with Standish’s phone in the trunk and just barely hid it when Patrice came to retrieve him and lead him to an unexpected secondary location: The Lighterman pub in Granary Square.

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The finale features exceptional location shoots at Granary Square and King’s Cross, but why was River led past performing fountains, crowds of people, and bustling businesses to a lovely sit-down restaurant? So he could take a seat across from Harkness and have the chilling “Hello, dad. Hello, son.” talk at long last.

For those who are late to the big jaw-dropping reveal, allow River to spell it out for you. “I saw a painting on the wall,” he told Harkness, referencing the property where they first met. “It looked identical to pictures my mother sent me after 7th, 8th, and 9th birthdays. They stopped coming after that. It made me think she’d been there, but I didn’t know why.”

River questioned his biological dad, asking if he was ever in love with his mom or simply used her to breed. While Harkness said she was in love with him, he admittedly used her “to secure funds” and suggested River ask his grandfather for the details. As for why Harkness suddenly felt the need to drop in on River’s life, he claims he wanted to see if River was happy at Slough House and was hopeful that he’d rather work for the family business. “I don’t want fucking anything to do with you,” a frazzled River assured him. “I want you locked up. You’re a fucking maniac. I already have a job.” In wake of the harsh words, Harkness stressed that River is under-appreciated by the Slow Horses before sharing some unsolicited advice to help him up his spy game: Learn to think counterintuitively. Attack when you’re the target, and stand still while being pursued.

As River fiddled with Standish’s phone under the table, he rejected his dad’s Ted Talk and revealed he had zero regrets “about not being raised as a child soldier.” Proving he’s still one step ahead, Harkness clocked his son’s hidden cell and asked who he called. Without skipping a beat, River snapped back, “Childline” (a British counseling hotline for child abuse), which made his dear old dad cackle. In reality, he phoned Louisa, who — naturally — was already having Ho trace his whereabouts. (Shortly after Ho flexed his heroic tracking abilities, J.K. Coe helped him come to the crushing realization that his online girlfriend Kim was nothing more than a bot. The reveal may seem insignificant now, but showrunner Will Smith teased some serious Ho havoc in Season 5, so keep this tidbit filed away for later.)

After heading to Patrice’s shootout scene and checking in with Flyte, Louisa learned of the shoot to kill order out on River and realized where he was taken. While the women raced to the location from which River’s call was pinged, Marcus raced to buy back the gun he’d sold in hopes of protecting Slough House, and Lamb raced to his old pal Sam Chapman’s (Sean Gilder) office only to discover that Patrice had beat him there. As Lamb silently processed the death of his old pal Chapman in a brilliantly heartbreaking way only Gary Oldman could, he listened to a message on his machine that confirmed David Cartwright was back at Slough House. Unfortunately, Patrice was listening in, too, so he finally knew where to head next.

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Back in the restaurant, Harkness was still trying to convince River to join the dark side. He even offered him a ticket to Europe and a place in his organization so he wouldn’t have to kill him, but River stood firm. Before the two could even begin to sort decades of differences, their father-son bonding time was cut short by the arrivals of the Dogs, who were fast approaching the building with plans to shoot and kill.

In true Slow Horses fashion, the show switched into high gear and played at one of its many strengths by jugging multiple heightened moments in parallel. At Slough House, Marcus returned with gun in hand just in time to deal with Patrice, who was primed to go on yet another killing spree in search of David Cartwright. As the men made terrifying use of the office staircase in a chaotic shootout, Standish, Moira (Joanna Scanlan), and Ho made their way up to Lamb’s office to keep David safe. With assists from Shirley and Coe (who threw a tea kettle of boiling water down the stairs as a weapon in a clutch move), the Slow Horses were able to make it to Lamb’s office. Rather than waiting like sitting ducks, however, Marcus volunteered to brave the office alone in hopes of finishing off Patrice and protecting his pals.

At the scene of Emergency #2, River and Harkness exited the restaurant to guns drawn, despite pleas from Louisa and Flyte for Dogs to stand down. In an unexpected twist, River’s daddy issues intensified when Harkness put his escape plan into motion and placed a grenade into his son’s hood before fleeing the scene. (Yes, he popped a baseball cap on his head to ensure he was incognito.) After Louisa neutralized the immediate threat to River’s life, another epic chase to the station commenced, with River (TV’s best runner) sprinting through the rainbow King’s Cross tunnel in a visually stunning spectacle.

As the Harkness pursuit intensified, so did the situation at Slough House. Shortly after Marcus left to be the hero, the group seeking safety in Lamb’s office heard a harrowing gunshot ring out. Since the shootout was out of sight, it was unclear if the bullet took out Marcus or Patrice, but Shirley snatched Lamb’s gun just to be safe. Seconds of suspense mounted before their greatest fears were realized. Patrice arrived to attack, which meant that Marcus was likely down for the count. Following a fleeting flicker of grief, Shirley sprung into action and fired back at Harkness’ man, only to swiftly run out of bullets. The Slow Horses were officially stuck, but as we saw earlier in the season, when his team hits rock bottom, Lamb swoops in to pull them back up.

With the Dogs, Louisa, and River losing breath trying to track down Harkness, River unexpectedly stopped sprinting and had an epiphany. He remembered his dad’s advice from earlier, headed to a nearby station bar, and sat down next to Harkness, saying, “What was it? When you’re being pursued stand still?” Sure, Harkness’ plan was blown. But he had to respect his son for outsmarting him. He shot River a smile, drew his gun, then spun it around and handed it over in defeat, saying, “Good job son.” In one of the season’s greatest lines, River snapped back, “You just put a grenade in my hood, don’t fucking son me.” For someone being cuffed and taken away for major crimes, Harkness seemed eerily chill and confident, smoothly suggesting, “I’ll take the later train.” In a rare moment of Season 4 serenity, Louisa sat down beside River to ask “who the fuck is that?” River simply replied, “My dad,” before cathartically chugging a glass of wine and swallowing the hard truth.

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Lamb indeed saved the day again, arriving just in time to disarm Patrice before he obliterated the majority of the Slow Horses. Tragically, he arrived too late to defend Marcus, which Shirley knew deep down as raced to find her partner. The team handcuffed Patrice to a radiator, and though David Cartwright was safe, Lamb received a concerning call from Molly (Naomi Wirthner), who had something he needed to see — presumably the message that Harkness needed her to send. When a distraught Shirley returned with confirmation of Marcus’ death, she readied herself to kill Patrice, only to be stopped by Coe, who uttered one of the show’s most heartbreaking lines: “He loved you and he wanted you to love yourself.” When Coe successfully set Shirley free from a murder, he took matters into his own hands and killed Patrice himself before putting his headphones on and heading out.

Despite the unbearable Slough House hurt, the Slow Horses (particularly River) could at least rest easier knowing Frank Harkness was in custody…or was he? Shortly after Diana arrived for his interrogation, Harkness said he had plans to rebuild his operation and take River off their hands. “You’re gonna find out it’s all starting all over for me. I left a failsafe, never thought I’d have to use it,” he said with a smile. Just then, Diana got called outside for an urgent matter. Next time we saw her, she was at Slough House checking in with a rattled Lamb who got Harkness’ failsafe from Molly: letters to the heads of services. The Park had 12 hours to let Harkness go, or the letters that detailed the dirty work he’d done for them for years would go up on the web.

Initially, Diana seemed deeply distressed, but while realizing the mess was Claude’s to clean up, she shared a “marriage of convenience” joke with Lamb and agreed to his pleas to bump Marcus’ post-death payout to 10 years salary — that of an active duty agent — to ensure his family was cared for.

At the Park, Harkness’ letters and presumed release wasn’t the only thing Claude had to worry about. After Ho helped Moira realize why she lost her job and got banished to Slough House, she headed to Claude’s office, demanded her job back (with a pay raise and four-day week), and threatened to tell everyone he was stopped for curb crawling. Terrified that his reputation and job were in jeopardy, Claude caved to her requests — and it sounds like much more Claude chaos awaits in Season 5.

Before the season wrapped, River was forced to reckon with the reality that on top of his biological father being a monster ex-CIA operative, he was losing a part of the only father figure he’d ever known: David Cartwright. Much to both of their dismays, River helped his grandfather get settled at a care home, because it was clearly unsafe for him to continue living on his own. A distraught David protested his freedom being stripped away and begged River to reconsider, but River stood strong, just barely waiting until he walked outside to break down.

Saved by the bell, River received a phone call that snapped him out of his emotional spiral. Who from? Lamb, who asked him to meet him at a bar. Why? To sign some operational bonus paperwork. Not to bond. The two had been through a lot, so Lamb told River he could join him for a drink, so long as he bought it himself and kept his mouth shut. With Nick Drake’s “Hazy Jane I” playing in the background, River sat down for a drink with his Third Dysfunctional Dad in what’s sure to be the calm before another Slow Horses storm.

Slow Horses Season 4 is now streaming on Apple TV+. Read on for everything we know about Slow Horses Season 5, and be sure to check out Decider’s interviews with showrunner Will Smith and star Kadiff Kirwan for more behind-the-scenes insights and teases.

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