Olivia Cooke Makes a Surprise Return in the Trailer for Slow Horses Season 6

Apple TV released the first trailer for Season 6 of its spy series Slow Horses, and tacked on the very end was the shocking (I gasped) return of Sidonie Baker, played by House of the Dragon’s Olivia Cooke. Cooke had a short-lived but beloved stint as Sid during Slow Horses’ premiere season in April 2022.

Viewers who also have read the source material, Mick Herron’s Slough House series of novels, knew that we’d just have to ride it out until the TV show caught up. The new trailer kicks off with a series staple in a tete-a-tete between Gary Oldman’s curmudgeonly Jackson Lamb, who looks after the home-for-remedial-MI6-spies Slough House, and Kristin Scott Thomas’s Diana Taverner, the current head of MI6.

It seems that the Slow Horses are the targets for the bad guys — one of whom is played by Andor’s Most Annoying Boy (complimentary) Kyle Soller — and Lamb attempts to herd the current staff and alumni of Slough House like cats to keep them all from getting murdered.

The trailer also highlights the welcome return of Louisa Guy, played by Rosalind Eleazar, after she promised she was leaving the espionage business entirely at the start of Season 5, and another showdown between River Cartwright (Jack Lowden, who might be promoted to Good Spy as he’s being eyed to be the new Bond) and his horrible, evil father, Frank Harkness (a particularly spooky Hugo Weaving).

Watch the trailer below: Not everyone will make it out of Slough House alive. #SlowHorses Season 6 premieres September 16. pic. twitter. com/uznKQ0VSAE — Apple TV (@AppleTV) August 18, 2026 Slow Horses has been cranking out seasons television yearly since it premiered — with the exception of Season 2, which came out less than a year after Season 1.

That’s old-school TV! Season 6 will adapt two books in Herron’s series, Joe Country and Slough House, instead of the typical one. Season 7 has already been greenlit. The first episode of Slow Horses Season 6 comes out September 16 on Apple TV with new episodes airing weekly.

Leanne Butkovic (she/they) is an Editorial Project Manager at IGN, where they've also written about TV, movies, and games.