Olivia Cooke returns to Slow Horses as Sid Baker after four-season absence

Apple TV+ released the Slow Horses Season 6 trailer on 18 August 2026, showing Olivia Cooke back as MI5 agent Sid Baker — last seen in the Season 1 finale. The six-episode season adapts Mick Herron's Joe Country and Slough House, premieres 16 September 2026, and features Gary Oldman, Kristin Scott Thomas and Jack Lowden.