Slow Horses Season 6 Finale Ends With River Cartwright's Apparent Death as Season 7 Trailer Debuts

The finale continued a season marked by a high number of character deaths. Flyte's killing at Harkness's hands was followed in the episode's final moments by a second death presented far more obliquely: River, whose cause of death is not made explicit on screen. Apple released the episode on its streaming service, and the season seven trailer aired immediately after it.

Showrunner and head writer Gaby Chiappe, speaking to Gold Derby, said the mechanism was set up in the second episode. In that scene, the assassins Jim and Jane, played by Kyle Soller and MyAnna Buring, knock on a door while River and Sid hide. Chiappe said viewers see Jim notice a small bottle lying on a table and the crowbar River had brought in with him.

"We have to assume that he paints it with what's in the bottle, which — given that there have been nerve agent attacks elsewhere — it's a Novichok attack," Chiappe said. She added that the production debated whether audiences would grasp what was happening, since the effect is deliberately peripheral. "It's still the idea that something happened in the corner of your eye, but you didn't quite know what it was," she said, noting that the assassin who planted the agent is by then long dead.

The device was adapted from the source novel, though Chiappe said the book leaves the substance on a doorknob, a difference from the television version. She did not state outright that River is dead; the season seven trailer points that way.

Apple has already renewed Slow Horses through season eight. Filming on season seven is complete, with a launch expected in or around September 2027.

Apple TV is priced at $14.99 per month and is also available through the Apple One bundle.