Slow Horses is a darkly humorous espionage drama that follows a dysfunctional team of British intelligence agents who serve in a dumping ground department of MI5 known, unaffectionately, as Slough House. Gary Oldman stars as Jackson Lamb, the brilliant but cantankerous leader of the spies, who end up in Slough House due to their career-ending mistakes. They also frequently find themselves blundering around the smoke and mirrors of the espionage world. Season six sees the Slow Horses on the run as Diana Taverner embroils them all in a fatally high-stakes game of retaliation and revenge.

The ensemble cast includes Academy Award nominee Kristin Scott Thomas, Emmy Award nominee Jack Lowden, Saskia Reeves, BAFTA Award nominee Christopher Chung, Aimee-Ffion Edwards, Rosalind Eleazar, Joanna Scanlan, BAFTA Award nominee Samuel West, Ruth Bradley, Tom Brooke, Academy Award nominee Jonathan Pryce and Hugo Weaving, alongside new addition BAFTA Award winner Lenny Rush. Additionally, Olivia Cooke reprises her role as Sidonie “Sid” Baker in the sixth season.