[Warning: The below contains MAJOR spoilers for the Slow Horses Season 4 finale “Hello Goodbye.”] Slow Horses stages the worst father-son reunion in the Season 4 finale for River ( Jack Lowden ). Jackson Lamb ( Gary Oldman ) as his father figure doesn’t look so bad anymore! It turns out mercenary Frank Harkness ( Hugo Weaving ) is River’s father—and he puts a grenade in the hood of his son’s jacket as MI5 is moving in! Frank does eventually end up in an interrogation room, but he’s not worried; he knows he won’t be spending too long there.
Meanwhile, Patrice’s (Tom Wozniczka) assault on Slough House results in Marcus’ (Kadiff Kirwan) death, and River moves his grandfather David ( Jonathan Pryce ) into a care home. Below, showrunner Will Smith talks about those and more major moments from the Season 4 finale and teases what’s ahead in Season 5. Talk about bringing in River’s father, what you wanted to do there, and where you wanted to leave River as a result of that.
Will Smith: The kind of arc of the season for River, and it is an interesting one. And one of the things I love about the show is each season has a different kind of emphasis, and obviously, you’re bringing in different characters and saying goodbye to some others—but it just felt really fresh and interesting to have a series where River is not in Slough House at all, has one scene with a Slow Horse, which is Louisa [Guy , who plays Rosalind], and then is on his own for the whole time. .
