Slow Horses season six has concluded with a major plot twist for a certain character – but are they really dead? Warning: I will be revealing spoilers for Slow Horses season six, as well as sharing information from the following novels by Mick Herron.

In the final moments of Slow Horses, it appeared that River Cartwright was finally having the tiniest bit of good luck when he realised that his love interest and fellow spy, Sidonie, had managed to escape Taverner's clutches and was at his grandfather's old house. However, upon entering the house and fussing around the kitchen, he briefly picks up a metal handle which appears to be impregnated with some sort of poison. This quickly renders him gasping for breath on the floor, while Syd continues to obliviously have a shower upstairs.

According to the books, no, he is not. River is poisoned with a nerve agent by the Russian hitmen who have been the main antagonists of season six, but he is not killed by the incident. Syd eventually finds him and gets help.

However, the attack leaves him with lasting side effects, including issues with his vision, fatigue, and feeling woozy. As such, in the eighth novel, Bad Actors, River is on medical leave while he recuperates.

Slow Horses stars in season six

While season seven is set to adapt the eighth novel – after season six merged two of the novels together – this would suggest that River will largely be missing from the new series. However, this could work well for the actor who portrays the hapless spy, Jack Lowden, who is widely rumoured to be playing the new James Bond.

Jack Lowden as River Cartwright in Slow Horses

While one of the key questions about the potential casting has been how Jack will play 007 while also filming Slow Horses (which was recently renewed for season eight), this character detail could temporarily give Jack a reduced role on the show while filming the movie. It's a win-win!

Gary Oldman as Jackson Lamb in Slow Horses

River returns to active duty by book nine, Clown Town, with the book's synopsis reading: "Slow horse River Cartwright is waiting to be passed fit for work. With time to kill, and with his grandfather – a legendary former spy – long dead, River investigates the secrets of the old man's library, and a mysteriously missing book."