Based on Mick Herron's Spook Street, season four premieres on Wednesday, September 4, followed by new episodes every Wednesday till October 9.
Season three ended with a bang, and the trailer once again shows the ensemble battling mighty explosions and tricky cases, as well as Lamb's penchant for swearing.
Gary Oldman stars in Slow Horses as Lamb, the brilliant but misanthropic leader of the spies, who are brought to Slough House for their career-ending mistakes, often blundering through the smoke and mirrors of the espionage world.
The returning ensemble cast also includes Academy Award nominee Kristin Scott Thomas, BAFTA Scotland Award winner Jack Lowden, Saskia Reeves, Rosalind Eleazar, Christopher Chung, Aimee-Ffion Edwards, Kadiff Kirwan and Academy Award nominee Jonathan Pryce.
Joanna Scanlan, Ruth Bradley, Tom Brooke and James Callis join the cast for season four. Season five has also already wrapped.
Slow Horses has made waves around the world, with season three nominated for nine Emmys, including Outstanding Drama Series and acting nominations for Oldman (Outstanding Actor in a Drama Series), Lowden (Outstanding Supporting Actor in a Drama Series), and Pryce (Outstanding Guest Actor in a Drama Series).
Slow Horses is produced by See-Saw Films and adapted for television by Will Smith. Jamie Laurenson, Hakan Kousetta, Iain Canning, Emile Sherman, Jane Robertson, Julian Stevens, Douglas Urbanski, Gail Mutrux, Graham Yost, and Smith are executive producers. Season four is directed by Adam Randall.
Watch the trailer below.