Read ‘Slow Horses’ Season 4 Finale Script By Will Smith

Editor’s note: Deadline’s It Starts on the Page (Drama) features 10 standout drama scripts in 2025 Emmy contention.

Season 4 of Apple TV+’s Slow Horses wrapped another taut tale from the world of Mick Herron’s spy novels with the episode “Hello Goodbye,” a poignant finale that has become the norm for series creator Will Smith, who has turned Herron’s books about the MI:5 gang that allegedly can’t shoot straight into must-watch TV.

Smith — the reigning Emmy winner in the drama writing category for Season 3 of Slow Horses, which landed nine noms overall, including Outstanding Drama Series — was nominated for a third consecutive USC Scripter Award this year for “Hello Goodbye.” The episode, directed by Adam Randall, includes the big reveal that the mercenary team wrecking havoc in London all season long is run by the father of River Cartwright (Jack Lowden) — a revelation that sets off the mad-dash sprint to the end that includes River’s estranged dad in question, Frank Harkness (Sam Neill), offering his son a job in the family business (before stuffing a grenade in his hoodie); a chase through the London subway tubes; Slough House being infiltrated by the most deadly of Frank’s men; and the eventual death of one of the Slow Horses‘ own in Marcus (Kadiff Kirwan).

Here is the script for “Hello Goodbye” with an intro by Smith, in which he reveals that Kirwan changed Marcus’ final line and how a Season 3 scene between River and his grandfather David (Jonathan Pryce) inspired him to write Season 4 finale’s heart-wrenching penultimate scene in which a conflicted River leaves dementia-stricken David in an assisted-living facility. Smith also explains why he ended the episode with River having a silent sit-down at the bar with another of his father figures, the curmudgeonly Jackson Lamb (Gary Oldman), which, in the world of Slow Horses, is what passes for a touching father-son moment both men need — and keeps the lights on for Season 5.

The Season 4 cast of Slow Horses also includes Saskia Reeves, Joanna Scanlan, Christopher Chung and Tom Brooke as Slough House staffers Catherine Standish, Moira Tregorian, Roddy Ho and J.K. Coe, respectively.

I was so excited when I finished Mick Herron’s Spook Street as I knew it would make for a terrific fourth season if we were lucky enough to get there. Having set up this backwater office where nothing ever happens and then bring death to the door was a brilliant stroke. Viewers and readers now know that Mick regularly dispatches beloved characters so once the lock is shot off and the door kicked in we fear for all the people in that building and we genuinely don’t know who is going to walk out alive.

Marcus’ death was a huge loss for the show, but Kadiff Kirwan made it even more poignant. On the page his last line to Shirley is “No, it’s my turn to save you.” But that felt too earnest, too on the nose, too like the sort of thing someone might say in a TV show. Kadiff suggested “Shirley, I got this.” It was simpler, tender, calmer and more heart-rending for Shirley who will spend series five dealing with her grief and guilt. That’s the thing about our departed cast, they’re still part of the show, they haunt the characters they’ve left behind.

Our director Adam Randall did an outstanding job across the series building to an incredible finale. The assault on Slough House has all the elements I love about the show ratcheted up. It has you laughing one moment then putting your hand over your mouth in shock the next. But the action and humour are always led by the characters. It makes sense that Catherine Standish will want to make sure all the available bullets are in the gun, I believe that Moira Tregorian is going to fall to pieces and lose the bullets, and of course Roddy Ho is going to flee upstairs and hide in the toilet under the guise of protecting David.

After the shooting stops and the dead have been counted we move on to quieter scenes that are no less seismic. I’m so proud that we can move people as much with a two-hander dialogue scene as we can with a car chase. The penultimate scene where River puts his grandfather in the home breaks my heart. I wrote it pretty much straight after watching Jonathan and Jack shoot the scene in series 3 where they both realise David is starting to succumb to dementia. I knew how deeply affecting they would be in a scene where they confront the reality of what David’s condition means for them. There was a question as to whether it was too sad. But I wanted to show that moment because it’s real. And because it honours the world that Mick created which has real and messy characters in a genre piece, spies being human like the rest of us.

After watching an anguished River walk away from his grandfather begging him not to leave him, we knew we needed a spark of light in the dark. As in the book, River is apart from the Slow Horses for most of the story. But I know the audience love watching Gary and Jack as much as Gary and Jack enjoy playing scenes together and so I wanted to give everyone a moment of Lamb and River. After a series arc in which River loses his grandfather, finds his father who he learns is a psychopath and then is left with Lamb as the only paternal figure in his life Lamb’s “Well you can stay and have a drink if you like. As long as you get your own and don’t say a f*cking word” feels like warmth. And in a sense it is. In the books Lamb is 100% bastard, but Gary gives him a sliver of heart. I think yes, he called River to get him to sign a form so Lamb could basically claim overtime. But he also knew that like him River would be alone and could maybe do with the gesture of some company. That’s why I love the character and love what Gary is doing with him. There are so many layers to unpeel, so many facets that are unexpected and at the same time make sense when revealed. Such as the final tender touch that Lamb gives to his dead friend Sam Chapman. That wasn’t on the page. Nor was Catherine’s shriek when Coe executes Patrice, nor the blank look on Coe’s face post-killing that verges on disappointment. That’s all from the actors, absolute marvels every one of them.

Will Smith

Read Smith’s script “Hello Goodbye” below.