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 un-affectionately as Slough House. Season four opens with a bombing that detonates personal secrets, rocking the already unstable foundations of Slough House.

Gary Oldman stars as Jackson Lamb, the brilliant but misanthropic leader of the spies. The spies end up in Slough House due to their career-ending mistakes, as they frequently find themselves blundering around the smoke and mirrors of the espionage world.

The returning ensemble cast includes Kristin Scott Thomas, Jack Lowden, Saskia Reeves, Rosalind Eleazar, Christopher Chung, Aimee-Ffion Edwards, Kadiff Kirwan and Jonathan Pryce.