When does Slow Horses return?

Slow Horses is a British spy thriller television series based on the Slough House novels by Mick Herron. The first series, Slow Horses, premiered on Apple TV+ on 1 April 2022. The programme was renewed for a third and fourth series. The fourth series, Spook Street, premiered in September 2024.
Slough House is an administrative purgatory for MI5 service rejects who have bungled their job but have not been sacked. Those consigned there are known as "slow horses" - a pun on "Slough House" They are expected to endure dull, paper-pushing tasks, along with occasional mental abuse from their miserable boss, Jackson Lamb.