Summary

• Slow Horses season 4 teases the death of one of Lamb's agents, but the source material suggests that River is unlikely to die.
• However, River's survival in the book doesn't guarantee the safety of other Slough House agents; the series is overdue for another major character death.
• Slow Horses may deviate from the novel and still kill off River, but this would require significant changes to future storylines and would surprise longtime fans.

Slow Horses season 4 is already teasing a major death, but the book that inspired the season may have already poked holes in that potential plot twist. Slow Horses is a spy thriller that's never afraid to play the adventures of Slough House for drama, tension, or unexpected comedy. This has benefited the series, which has become a critical darling for Apple TV+ over the last three seasons.

Slow Horses focuses on Slough House, a ragtag band of MI5 agents who've been assigned to a team commanded by the slovenly but brilliant Jackson Lamb (Gary Oldman) after making embarrassing mistakes in Britain's premier spy agency. The gags don't detract from the inherent danger of the setting, and multiple characters having perished in previous seasons. The trailer for Slow Horses season 4 teases another of Lamb's agents will die. However, the book that inspired the season includes a fake-out death that suggests at least one character will escape the season's event alive.

Lamb Deliberately Misidentifies River's Body In Slow Horses Book 4

The trailer for Slow Horses season 4 hints that one of Lamb's agents will be killed in the line of duty, but the source material makes it unlikely that River (Jack Lowden) will die. River is one of the most prominent agents at Slough House, a promising figure whose career was derailed by a very public training exercise gone wrong. Slow Horses season 4 is set to adapt Spook Street, the fourth book in the Slough House series of novels. Spook Street focuses on the fallout of a bombing in London that shakes MI5.

River is a major player in the novel, balancing his spy work with the faculties of his grandfather David (Jonathan Pryce). In the novel, River is briefly thought to be dead, with Lamb identifying his body. However, this turns out to be a misdirection from Lamb, allowing River to continue his investigation. Given this plot turn in the source material and River's central role in the show, it makes his death in Slow Horses season 4 (and subsequent absence from the Slow Horses season 5) unlikely. This doesn't mean audiences should expect things to be easy for Slough House.

Slow Horses Season 4 Could Still Kill Off A Character

Just because River survives in the book doesn't mean that a Slough House agent won't be killed off in Slow Horses season 4. Slow Horses has racked up several deaths, including Jed in season 1 (while the comatose Sid's fate remains a mystery). Season 2 similarly killed off Min. Slow Horses season 3 broke this tradition by not killing any major characters. In this way, Slough House is overdue for another death in Slow Horses season 4. The Slow Horses season 4 trailer places multiple characters in the cross-hairs and ends with Lamb seemingly revealing one of his team has died.

This could refer to any number of agents and could be adapting River's fake-out death from Spook Street. It's also possible that the season deviates from the novel and does kill River. That kind of plot twist would necessitate several changes to future stories given River's prominent role. It wouldn't be the first time the show has changed the plot, however, as Whelan's absence impacts the plot of season 4. The Spook Street story makes it unlikely that River will be slain, but the twisty world of espionage featured in Slow Horses could catch even longtime fans by surprise.

Seasons 1-3 of Slow Horses are now streaming on Apple TV+. Season 4 is expected to arrive on the streaming platform sometime in 2024.