SLough House, the building where the ragtag team of spies work in Slow Horses, is not a peaceful place. The interior is run-down, the decor is full of mid-century fashion, the office gossip is neither respectful nor constructive, and by the end of the new season of Apple TV+’s prestige spy drama, the windows are smashed and the walls are riddled with bullet holes.

Slow Horses, however, is a pleasant show to fall back on. Discerning viewers, pleased with their own excellent taste, will delight in a series led by the sheer quality of Gary Oldman and Kristin Scott Thomas, reminiscent of classic spy thrillers — intelligence work is a great battle of wits, played by capable misfits who care more about winning the game than the real-world consequences — while modernizing the spies’ espionage to make them sound like disillusioned cynics in an Armando Iannucci comedy. The recipe worked; Slow Horses is a word-of-mouth hit. But this is season four, and that’s the point where a winning formula can feel formulaic. Can Slow Horses keep it up?

The series’ return is familiar in many ways. Two things happen right at the start. River Cartwright (Jack Lowden), the closest thing to a traditional pin-up hero, expresses concern about his grandfather, the old-fashioned spy chief David (Jonathan Pryce), whose dementia is getting worse. Meanwhile, a London shopping centre is attacked by a suicide bomber. By now we know that these events will somehow prove not to be unrelated.

Another major conspiracy will be spun and then revealed, with the misfits banished to the purgatory of Slough House staying one step ahead of their supposed superiors at MI5 headquarters. All the old headlines are ready to go. There will be scenes where a villain is lurking somewhere and we don’t know when he’s going to jump out and attack the secret agent. There will be scenes where the secret agent is locked in hand-to-hand combat with a seemingly invincible villain and they come up with some strange method of survival. There will be scenes where the villains trap the secret agent in an office or bathroom, but by the time they kick the door down, the secret agent has jumped out of the window just in time. There will, and this is an absolute certainty, be scenes where a secret agent is either chasing or being chased through a crowd of London commuters and they have to clear passers-by out of the way.

Aside from the deceptively expensive shabby chic and the impeccable direction, Slow Horses often remains closely tied to genre cliches. But it never gets boring and the new episodes benefit from fresh blood in the already luxurious cast. James Callis, who was one of the best devious egomaniacs on TV as Gaius Baltar in Battlestar Galactica, plays another smooth weasel in the form of the new MI5 chief Claude Whelan. The agent obviously got his job by appealing to the stiff-asses in Westminster (“My job is to activate accountability and accessibility – that’s the triple-A promise”), but now has to manage his ice-cold deputy Diana Taverner (Scott Thomas, wonderfully edgy and devastating). Hugo Weaving, last seen as a reluctant softie in the wry Australian comedy-drama Love Me, is as far from reluctant or soft as he can be as the season’s villain, mercenary Frank Harkness. Ruth Bradley is excellent as Emma Flyte, MI5’s new attack dog; Joanna Scanlan is perfectly cast as Moira, an unstoppably fussy administrator; Tom Brooke is a disturbing wild card as JK Coe, a newbie who says and does almost nothing but has a brutal impact when he springs to life.

Slow Horses’ core cast has also slowly evolved. The first thing newcomers notice is Oldman’s portrayal of Jackson Lamb, Slough House’s monstrously jaded and raincoat-clad ruler who shuffles and roars like a bear dipped in French fry grease. A season or two ago, however, the showrunners realized he was wasted in more ways than one: He couldn’t sit in his smelly old chair so much, chugging corner-shop whiskey and being verbosely rude to his underlings. The process of sending him out into the field, where he can be a little more human and a lot more deadly, continues this year as the show successfully searches for new nuance and depth.

Lamb is involved in one of two unexpectedly beautiful interactions between long-time cast members – love stories shrouded in deep secrecy – that sneak up on viewers swept up in all the quips and gunfights but willing to take care of the weirdos of Slough House even when those scruffy villains refuse to take care of themselves. “Slow Horses” may still be a safe bet, but it’s not quite the same as it always was.