Slow Horses Season 6 Premiere Opens With Murder and Family Confrontation

The Season 6 premiere of the Apple TV+ series "Slow Horses" opens with the murder of former Slough House agent Struan Loy, establishing a new threat targeting past members of the disreputable MI5 unit. The episode, which aired on September 16, 2026, also confirms the death of David Cartwright, the grandfather of protagonist River Cartwright, and reintroduces his estranged father, Frank Harkness, as a disruptive presence. The premiere begins with Struan Loy, who had been living in a converted shipping container, being killed by two assassins posing as investors. The pair beat him and set the container on fire, securing the doors from the outside to prevent his escape. Shortly after, another former Slough House agent, Kay White, is murdered by the same duo, who drown her. Their conversation identifies River Cartwright as their next target. River spends much of the episode preparing for the funeral of his grandfather, David Cartwright, who died peacefully in an assisted living facility between seasons.