Robert Frost on Editing for the Espionage Dramedy 'Slow Horses'

In the eagerly anticipated fourth season of Slow Horses, the espionage dramedy continues to captivate audiences with its blend of suspense, humor, and human vulnerability. Based on Mick Herron’s Slough House novels, the series follows the misfits of MI5, led by the indomitable Jackson Lamb, portrayed by Academy Award-winner Gary Oldman.

As they navigate the drudgery of administrative work, they learn that escaping past mistakes is never easy. This six-episode season premieres on Apple TV+ on September 4, with new episodes every Wednesday until October 9.

In this insightful interview, we speak with Robert Frost, the talented television and film editor behind Season 4. Robert shares his experiences and challenges in bringing the latest season of Slow Horses to life, offering a glimpse into the meticulous process of balancing multiple genres and editing for this critically acclaimed series.

Editor's note: the following interview is edited for length and clarity.

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No Film School: What drew you to the editing role for Slow Horses?

Robert Frost: I’m a huge fan of the show and had already watched the first two seasons when the chance to join for Season 4 came up. I decided to dive into the books and tore through them, completely falling in love with the characters. Will Smith does an amazing job bringing the books to life on screen—each script is fast-paced, full of character, and perfectly blends spy action with British humor. Adam Randall and I found we had very similar taste and referenced the same shows and movies, so it seemed like a no brainer.

NFS: How did you collaborate with director Adam Randall and writer Will Smith during the editing process?

Frost: There’s a fun action sequence in a later episode, for which Adam suggested it’d be helpful if I came down to the location and edited the scene as it was being filmed. This allowed Adam, Will, and me to collaborate more closely than is typically possible during the early assembling process.

It’s an action sequence with some complex choreography. After a setup was complete I’d grab the material from the camera team and cut it into the sequence. Adam and Will would review the scene as it evolved over several night shoots. We were able to see very quickly which beats were landing (and which could be better). To have the edit directly inform how the shoot progressed was really fun, Adam was able to press ahead with confidence knowing exactly what pickups we needed, whether we owed reactions or cutaways or if he was happy with what we had.

When it comes to action sequences, despite the chaos that comes with the violence, you still want to make it very clear what is happening to who, where everyone is in relation to each other, what the characters need to do to ‘win’. You don’t want the audience wondering, “Why don’t they just do this?” or “Why isn’t that character helping?” To avoid confusion, we often add ADR to clarify plot points or have the second unit shoot additional inserts. But by editing on location, Will could watch the scene and write new lines on the spot, while Adam could revise his shot list, and we would then grab the extra pieces we needed.

A nice bonus of being on set was the opportunity to share the sequence with some of the cast and crew. I don’t have the patience of the production crew, who work tirelessly on a project and don’t see the end results for months if not years! So it was nice to gather everyone around the macbook at 3am in the freezing cold and show them what they had been working so hard on.

'Slow Horses'Apple

NFS: What unique challenges did you face when editing scenes shot months apart?

Frost: I’ve always had a bit of a gripe with phone conversation scenes in film and TV—they can easily end up being quite dull to watch! They’re a staple of the thriller genre, along with those scenes where characters huddle around monitors reacting to what’s happening on the screens. Slow Horses has plenty of these! One challenge with these scenes is that the two sides of a phone call are often filmed months apart. For instance, in episode one, Taverner and Whelan are watching a raid on a block of flats, but they are reacting to action that will be shot much later.

Patience is key when piecing together these scenes, and it takes some faith to present a cut full of gaps, trusting that it will all come together in the end. Once you have all the footage, the challenge is finding an elegant path through the scene. Even if you’ve got amazing coverage of Kristen Scott Thomas and James Callis (there were hours of fantastic material!), you have to analyze the scene beat by beat, as it might better serve the story to focus on the SWAT team instead. A scene with Lamb may play brilliantly by just holding on to him for the entire phone conversation, and it’s tempting to stick with that approach after it’s been in the cut for a while. But once you get to the other side of the scene, you’d be doing yourself a disservice if you don’t reconsider and rebuild the scene from scratch. Like with most scenes, I’ve found that the key is iteration; every few days I’d revisit the sequence, tweaking and refining, swapping out or cutting shots, until eventually it flows.

NFS: How does Slow Horses balance drama, suspense, and comedy, and how did you reflect this in your editing?

Frost: A lot of the show’s unique tone comes from the writing, direction, and performances. From an editing perspective, you usually start to see these different flavors emerge when you’re putting together the initial editor's cut. That’s when you begin to get a feel for the balance of each episode.

In the first episode, there’s a scene where the gang at Slough House receives some terrible news, only for the mood to abruptly flip into comedy. We kept getting feedback that the humor wasn’t landing quite right, and ultimately, the fix was as simple as swapping out a single shot—maybe a second long—for a different take. It’s a great example of how a small tweak can address what seemed like a bigger issue. It took us a while to get there, though, because we were initially attached to a performance we loved. I generally try to protect the original choices from the director's cut, but in this case, going back to the rushes and swapping out a reaction made a huge difference in the scene's tonal shift.

In a later episode, there’s a moment where Lamb enters Slough House and trudges upstairs to his top-floor office. This was followed by three consecutive scenes of brilliant Lamb dialogue—some top-tier put-downs! But in the end, we decided to cut one of the scenes, even though it meant losing one of my favorite lines from the series. It became clear that we were overstaying our welcome in the ‘workplace comedy’ aspect of the show, and we needed to shift the focus back to the drama.

Robert FrostImpact24

NFS: Can you discuss a specific editing decision that significantly impacted a scene's emotional tone?

Frost: In episode one, Lamb arrives at a crime scene—the death of a colleague. He’s his usual acerbic, flatulent self, with Gary Oldman delivering a brilliant performance that suggests he’d rather be anywhere else. This scene also marks the first time we meet Flyte, MI5’s new 'head dog,' and cutting their back-and-forth was a blast—it’s just one zinger after another!

But it’s also a pivotal story moment, with this death being crucial to the season’s plot. The hope is that the audience feels a real sense of shock. There’s a moment where Lamb crouches down to inspect the body up close, and in one particularly powerful take, Gary Oldman gives just a flicker of vulnerability, almost letting Lamb’s facade slip. We experimented with other takes and had plenty of coverage to approach the scene differently, but from the start, Adam and I knew that holding on Lamb was the most powerful choice.

There was some understandable pushback—questions about whether the shot was too long, too subjective, or if showing Lamb let his guard down made sense within the larger story. But ultimately, we kept it, and I love how that single shot, with its silence and lack of wisecracks, brings a mournful gravitas to the scene amidst the comedy. It’s one of my favorite moments of the season.

NFS: What was the most rewarding part of working on Slow Horses Season 4?

Frost: As an editor, I have the unique privilege of being one of the first to see each episode come together, and that’s what makes the job so exciting. It’s incredibly rewarding to take everyone’s hard work and piece it together into something cohesive. I’m genuinely a fan of both the series and the novels. Getting to be a part of telling these stories and working with such an amazing crew is the best part of the job.