Spoilers for Slow Horses seasons 1-4 follow.

The only reliable thing about Jackson Lamb and his squadron of semi-competent MI5 agents is that they will always be back for another season.

Everyone still alive after season four is busy wiping down the walls and taping over the broken windows as they prepare for season five (an adaptation of Mick Herron’s fifth book in the series, London Rules).

We’re also levitating with excitement over the news that Apple TV+ has greenlit season six and will adapt books six and seven, Joe Country and Slough House.

So what can we expect?

First things first, it’s a definite that Slow Horses will return. Apple TV+ (officially one of our best streaming services) confirmed that a fifth season was commissioned back in January 2024 and a sixth season is on the way too. Slow Horses is as close to a bankable hit as TV gets right now, and Apple TV+ is very happy to be the bank in question.

But when will we see it? While season one debuted in April 2022, seasons two and three came out in December of ’22 and ’23 respectively, while the fourth season came a little earlier in September ’24.

If we were to assume an annual autumn release window and a year-long production schedule, that means we could reasonably expect the fifth season around September 2025.

Gary Oldman confirmed in August that season five was already in the can, telling Deadline: “We’ve just finished filming season five and there’s another layer of the onion that is peeled back with Lamb. You find out a little bit more about what went on.”

They don’t hang about on this show – while they were shooting season four, they were writing season five, and when they were editing four, they were shooting five. (Which means that they’re editing five now and writing six.)

That all being so, assuming a maximum six-month editing/post-production cycle, we might see the fifth season arrive earlier in the year than usual, possibly even in the spring of 2025. But that depends on Apple TV+’s corporate plans and complex variables like awards windows: they wouldn’t want season four to compete with season five for the same categories, so post-June is more likely.

There’s no show without Gary Oldman as walking binbag Jackson Lamb. Luckily he’s confirmed he’ll be around until they stop making the show.

Jack Lowden, who plays River Cartwright, revealed a similar outlook to Collider: “As long as it’s still interesting and people are still interested, I think it’s the same with anything. I’d love to do it.”

Alas, Marcus Longridge didn’t make it out of season four, so it’s the last we’ve seen of Kadiff Kirwan around the Barbican. Joanna Scanlan’s role as busybody Moira Tregorian looks like a one-and-done, so she too is probably not returning.

Here’s who’ll be back to join Oldman and Lowden if all goes to plan:

• Saskia Reeves as Catherine Standish
• Christopher Chung as Roddy Ho
• Rosalind Eleazar as Louisa Guy
• Kristin Scott Thomas as Diana Taverner
• Aimee-Ffion Edwards as Shirley Dander
• Naomi Wirthner as Molly Doran
• Ruth Bradley as Emma Flyte
• Tom Brooke as JK Coe
• James Callis as Claude Whelan
• Samuel West as Peter Judd

As surely as night follows day and as an unidentifiable smell follows Jackson Lamb, the fifth season will, as we said earlier, follow Mick Herron’s book series, meaning the plot will be lifted from book five, London Rules.

This means the return of political intrigues involving Samuel West’s Peter Judd (and other populist politicians who we couldn’t possibly connect to any real-life figures), a string of mysterious terror attacks across the country and big trouble for the beleaguered First Desk Claude Whelan.

Much of this was confirmed in the teaser trailer that dropped at the end of the season-four finale, though there appear to be some interesting changes from the book that we won’t go into here for fear of spoilers.

Plus, there’ll be inappropriate humour and botty-burps in (and at) large volume from Jackson Lamb.

As mentioned above, season six has been confirmed and will adapt books six and seven. That’s the first time they’ve mapped more than one book to one season, so what gives? It could, of course, be a simple editorial choice.

Perhaps showrunner Will Smith believes that the stories are slight enough – and compatible enough – to be combined into one season. Maybe it just works better. That’s the most likely explanation.

Having said that, call us paranoid spooks chasing shadows, but we couldn’t help but observe that there are only eight books so far in Mick Herron’s series, and that the standard TV biz contract for main cast members in a TV show lasts for seven seasons before renegotiation comes due. (And, if the show is a hit – like Friends, say, or The Big Bang Theory – everyone gets major pay hikes.)

All this means that after seven seasons, Apple TV+’s budget for the show would have to expand significantly. That, perhaps, could be seen as motivation to end on the seventh season before things get stale and super-expensive. And the best way to make seven seasons out of eight books? Combine two of them.

Like we say – it’s paranoid conspiracy-talk, but we’d be remiss if we didn’t factor what we know about the TV business into our speculation.

As we mentioned above, there is a teaser at the end of the season-four finale, but Apple TV+ haven’t made it widely available beyond their streaming platform.

While we might not have an official version of the teaser, some diehard fans – or Slow Horses good samaritans) – have shared the clip to X (formerly known as Twitter) in the meantime.

View full post on X

So you can get a sense of what’s to come when the next season does finally arrive. Before then, Apple TV+ will release a full trailer so we can get an even better look at the upcoming action.