‘Slow Horses’ Season 4 Finale: How [SPOILER] Death Concluded ‘A More Raw, More Brutal, Harder Season’

SPOILER ALERT: The following story contains plot details from “Hello Goodbye,” the Season 4 finale of “Slow Horses.”

“Slow Horses” is not, as a rule, a sentimental show. Deceptively disheveled spymaster Jackson Lamb’s (Gary Oldman) idea of caring for his “joes” is to negotiate up their active-duty death settlement on a bureaucratic technicality. Yet the Emmy-winning Apple show’s fourth season, which concluded on Wednesday, was its most personal yet. River Cartwright (Jack Lowden) — a former MI5 golden boy whose exile to the series’ namesake box of broken toys established the show’s premise in Season 1 — began his latest misadventure by trying to save his dementia-afflicted grandfather David (Jonathan Pryce) — and ended it by coming face-to-face with his father, a sociopathic American mercenary named Frank Harkness (Hugo Weaving).

“What I love about Series 4 is that personal story,” says creator and showrunner Will Smith (not that one!), a comedian and frequent collaborator of Armando Iannucci. “It’s a more raw, more brutal, harder season.” And he knew just who to call to be the face of that new brutality: Weaving, Smith’s own first cousin once removed.

Despite the family connection, Weaving — who’d already played a legendary villain in Agent Smith of the “Matrix” franchise — hadn’t watched “Slow Horses” by the time he was sent the scripts. The series is adapted from British author Mick Herron’s eponymous set of spy novels, with each tightly structured, six-episode season corresponding to a specific book. Season 4 is based on “Spook Street,” the Herron volume that introduces Frank as what Weaving dubs “a Moriarty figure”: an archnemesis who can transcend individual storylines, serving as the kind of recurring adversary “Slow Horses” had previously lacked. (Unless you count the unfeeling bureaucracy of MI5 proper, as symbolized by Kristin Scott Thomas’ icy Diana Taverner.) 

An ex-CIA agent, Harkness has developed a unique approach to recruiting his private militia. Having fathered sons by several different women, he’s raised them from birth to become perfect killing machines at a compound in Lavandes, France. River’s own mother was seduced to give Frank leverage over David, a former higher-up at MI5; to negotiate his pregnant daughter’s release, David gave Frank a cache of authentic British passports issued to false identities, also known as “cold bodies.” One of these cold bodies was behind the shopping center bombing that opened the season — not an ideologically motivated act of terrorism, but a deadly form of acting out by a son against his father. 

“He’s usually a step ahead,” Weaving says of his character. “But obviously, there’s been a massive fuck-up with regard to the bombing.” It simply wouldn’t be very “Slow Horses” for anyone to be too competent, including a Big Bad. Weaving compares Frank to Saturn devouring his sons, the classical myth where a Titan eats his young to prevent them from replacing him. “If we say everyone has a fatal flaw, what would Frank’s be? He’s a father,” Weaving says. “So he has to be, in some way, both a nurturer and a teacher and a castigator.”

Weaving stresses that he didn’t want Frank to come across as a “ghastly inhuman beast.” On some level, the actor insists, Frank does love his sons. “I was most eager to make sure we maintain humanity even in an extreme situation,” he says. “We need to maintain a sense of Frank as a human being and as a real father, even if his sons are doing extreme things on his behalf and killing people.” When Frank offers River a job in the middle of a crowded restaurant, it’s both “utterly preposterous” and closely followed by a death threat. “But you need to feel that, for Frank, there’s a genuine human need.”

That one-on-one conversation is closely followed by a showstopper of a chase sequence through London’s iconic St. Pancras Station, overseen by the season’s director Adam Randall, and secured by location manager Ian Pollington. “Originally in the book, it’s by the Thames, and River falls in the Thames,” Smith says. Dunking River in the Thames is a nice opportunity for a pun, he adds, “but it’s tremendously expensive and also dangerous.” So the production pivoted to a scene that sees River internalize Frank’s advice to stand still when being pursued. He finds his father quietly sitting in a booth, where he’s apprehended peacefully — though not for long. When the MI5 top brass discover he’s assembled kompromat on the entire leadership, Frank is released offscreen, a typically Pyrrhic victory for the Slough House crew.

Meanwhile, River checks David into an assisted care facility, much to David’s anger and resentment. The scene is a painfully ordinary form of familial strife, but with an extraordinary twist: the facility itself is owned by MI5 and packed with retired spooks. “I just like the idea — and I’m pretty sure that’s in the book as well — that it’s safer for them all to be together, so if they just start blabbing, it doesn’t really matter,” Smith says. Pryce will continue to be a part of the show, opening up an intriguing new avenue for subplots.

To channel the spirit of page-turning genre fiction, “Slow Horses” is produced at a rapid clip. “I was doing the room for Series 5 as we were doing the prep and the start of the shoot of Series 4, and as the edits were coming in for Series 3,” Smith recounts, using the British term for TV seasons. This pace allows “Slow Horses” a regular release schedule at odds with the more relaxed rhythms of modern prestige television. 

That means Season 5 is already in the works. Smith won’t reveal too many specifics, but he promises the next episodes will trace the impact of Season 4’s events on both River and Shirley (Aimee Ffion-Edwards), who’s grappling with the loss of her frequent mission partner Marcus Longridge (Kadiff Kirwan) who’s killed by one of Frank’s son-soldiers during a tense shootout at Slough House HQ. “That’s what I love about what Mick does,” Smith says about killing characters off. “He doesn’t do it lightly, and he’s got an eye on the impact of the death.”

As for Frank, Weaving is playing his cards close to the chest. “Suffice it to say, Frank comes back in another book, and I’m in London at the moment,” he says.