Apple TV has released the first trailer for Season 6 of its spy drama Slow Horses, teasing a surprise return for Olivia Cooke as Sidonie "Sid" Baker, a character who left the show under dramatic circumstances after its debut season in 2022. The reveal, tucked at the end of the trailer, has excited fans who have long speculated about Sid's fate, since her storyline was never fully resolved on screen and readers of Mick Herron's source novels knew a return was possible.

The trailer also shows Rosalind Eleazar's Louisa Guy back in the fold despite vowing to quit the spy world, alongside series regulars Gary Oldman, Kristin Scott Thomas and Jack Lowden, plus new cast member Kyle Soller as an apparent antagonist. Season 6 will adapt two of Herron's novels, Joe Country and Slough House, rather than the usual single book, and premieres on Apple TV on 16 September 2026 with weekly episodes; a seventh season has already been confirmed.