Apple TV has released the first trailer for the sixth season of Slow Horses, setting up another bruising, darkly funny mission for MI5’s least polished spies. The six-episode season begins streaming globally on September 16, with new episodes arriving weekly through October 21.

For a show built around washed-up agents, stale offices and institutional contempt, Slow Horses has become one of the most dependable prestige dramas in streaming. Its secret has never been glamorous spycraft alone. The series works because it treats espionage as an ugly, bureaucratic, occasionally ridiculous business – one in which career-ending mistakes do not necessarily keep people away from national-security disasters.

At the heart of that mess is Jackson Lamb, the foul-mouthed, strategically brilliant head of Slough House, once again played by Gary Oldman. Lamb’s agents are the people MI5 would prefer to forget: damaged, distracted, insubordinate and frequently underestimated. Yet, season after season, those supposed failures have become the last line of defense when the more polished parts of British intelligence get things badly wrong.

Season six looks set to put that formula under greater strain. Apple says the Slow Horses find themselves on the run after MI5 power player Diana Taverner draws them into a dangerous cycle of retaliation and revenge. That premise suggests a more personal, less contained threat than the team’s usual accidental plunge into a wider conspiracy – and it gives the new trailer the tense, hunted feeling viewers have come to expect from the series.

The new season adapts material from Joe Country and Slough House, the sixth and seventh novels in Mick Herron’s acclaimed Slough House book series. That is a notable shift for the show, which has generally treated each season as a compact adaptation of one novel. Folding two books into a six-episode run could allow the series to move faster while pushing deeper into the consequences of the conflicts that have been building around Lamb, Taverner and the wider intelligence establishment.

There is also a welcome return for Olivia Cooke, who reprises her role as Sidonie “Sid” Baker. Sid has been one of the show’s most intriguing absences, partly because she was among the rare Slough House agents who seemed capable of operating comfortably outside its neglected confines. Her reappearance gives the series an opportunity to revisit an unfinished thread without losing the rough-edged group dynamic that has defined the show from the beginning.

The core ensemble remains unusually strong. Kristin Scott Thomas returns as Diana Taverner, the MI5 operator whose battles with Lamb are as entertaining as any car chase, while Jack Lowden, Saskia Reeves, Christopher Chung, Aimee-Ffion Edwards, Rosalind Eleazar, Joanna Scanlan, Samuel West, Ruth Bradley, Tom Brooke, Jonathan Pryce and Hugo Weaving are also among the returning cast. BAFTA-winning actor Lenny Rush joins the series for the new season.

That depth matters because Slow Horses has always been more ensemble-driven than its marketing might imply. Oldman’s Lamb is the gravitational center: disgusting, funny and often several moves ahead of everyone else. But the show’s real texture comes from watching its other agents try to navigate trauma, ambition, resentment and the very reasonable fear that their boss may be deliberately making their lives worse. The series understands that a workplace can be funny precisely because it is dysfunctional, even when that workplace happens to handle classified information and occasional gunfire.

Apple has also made an unusually aggressive long-term bet on the property. Season six arrives after five seasons that have consistently earned strong critical reception, and Apple says the show has secured Certified Fresh scores for all five, including perfect 100 percent critics’ scores for two seasons. Its fifth season received nine Primetime Emmy nominations, including Outstanding Drama Series, with acting nominations for Oldman and Lowden.

That consistency has made Slow Horses valuable beyond its awards profile. In the increasingly crowded streaming market, it is difficult to establish a returning drama that audiences trust to deliver each year without inflating itself into an event series. Slow Horses has managed exactly that. It is smart without being showy, grim without becoming joyless, and serious about stakes without pretending its characters are always heroic.

Season six arrives at a moment when Apple TV has a growing bench of high-profile dramas, but Slow Horses remains distinctive. It has neither the puzzle-box mystique of Severance nor the sci-fi scale of other streaming tentpoles. Its appeal is more grounded: sharp writing, expertly calibrated tension and a lead performance that turns every insult and disheveled entrance into a small event.

Adam Randall returns to direct the new season, while Gaby Chiappe adapts it for television. The series continues to be produced by See-Saw Films, with Oldman among its executive producers.

For viewers who have somehow missed the show so far, the first five seasons are already available on Apple TV. For everyone else, the trailer is a welcome sign that Slough House is not getting cleaner, calmer or more professional anytime soon – which is exactly why it remains such a pleasure to visit.