Slow Horses Season 4: Release date, where to watch, cast, plot, what happened at the end of season 3

Starring Gary Oldman, Jack Lowden and Kristin Scott Thomas, it follows the adventures of a group of MI5 rejects who, rather than being sacked, have been sent to the purgatory of Slough House where they endure dull and repetitive work while being bullied by a dyspeptic boss - beautifully portrayed by Oldman.

While they aren’t meant to get involved in active duty, the disgraced spies somehow manage to get tangled up in schemes that threaten the security of Britain.

Earlier this year Slow Horses - which is based on a series of books by Mick Herron - was nominated for nine Emmy Awards, including acting nods for Gary Oldman, Jack Lowden and Jonathan Pryce.

Now the release of season 4 is imminent, here’s everything you need to know.

When will season 4 of Slow Horses be released?

The fourth season of Slow Horses will premiere on Wednesday, September 4, with the first episode dropping at 8am UK time.

The remaining five episodes will follow on a weekly basis, becoming available at 8am each Wednesday until the season finale on Wednesday, October 9.

Where can I watch Slow Horses?

Slow Horses is exclusive to the Apple TV+ streaming platform which costs £8.99 a month. All seasons are available to watch.

New customers can take advantage of a seven day free trial period - so if you can wait for a few weeks you can binge watch the whole thing for free.

Many Apple products also come with three months free Apple TV+ included, so it’s worth checking if you have a deal available.

What happened at the end of season 3 of Slow Horses?

A whole tangle of intriguing plotlines came together at the end of season 3, with plenty of cliffhangers to get fans excited for season 4.

Catherine Standish (Saskia Reeves) discovered that Jackson Lamb had been involved in the downfall of villainous former MI5 director-general Charles Partner (James Faulkner).

River (Jack Lowden) and Louisa (Rosalind Eleazar) remarkably managed to escape the facility, with Shirley (Aimee-Ffion Edwards) turning up in the nick of time to release them from a convenient hatch. Sean Donovan (Sope Dirisu) was killed by an MI5 agent. The files they were looking for made it out and were destroyed.

The last twist came when it was revealed that River leaked copies of the files he had kept in his car - fooling his grandfather - in order to ensure Ingrid Tearney (Sophie Okonedo) paid for having Alison Dunn (Katherine Waterston) killed.

What is the likely plot of season 4 of Slow Horses?

As is the case with previous seasons, the plot is based on the series of bestselling books by author Mick Herron.

Season 4 is based on the fifth book in the series, Spook Street, which was published in 2017.

Of course the screenwriters won’t necessarily copy the story entirely, but if you want a sneak preview, here’s the blurb for the book (without any massive spoilers):

“Twenty years retired from the Intelligence Service, David Cartwright still knows where all the bones are buried. But when he forgets that secrets are supposed to stay hidden, there's suddenly a target on his back.

The 'Old Bastard' raised his grandson to be a hero, not a slow horse. Now, far from joining the myths and legends of Spook Street, River Cartwright is part of Jackson Lamb's team of pen-pushing no-hopers at Slough House. Which doesn't mean he won't ditch everything and go rogue when his grandfather comes under threat.

Lamb worked with Cartwright back in the day, and knows better than most that this is no innocent old man. So when a panic button raises the alarm at Intelligence Service HQ, it's Lamb who's called on to identify the body. And it's Lamb who'll do whatever's necessary to protect an agent in peril.”

Who is in season 4 of Slow Horses?

All the familiar faces from the previous seasons will be returning, with notable additions being Hugo Weaving (The Matrix), Ruth Bradley (Primeval), James Callis (Battlestar Galactica), Joanna Scanlan (The Thick of It) and Tom Brooke (Empire of Light).

The full cast list - and character names - are as follows:

• Gary Oldman (Jackson Lamb)
• Kristin Scott Thomas (Diana Taverner)
• Jack Lowden (River Cartwright)
• Rosalind Eleazar (Louisa Guy)
• Christopher Chung (Roddy Ho)
• Aimee-Ffion Edwards (Shirley Dander)
• Kadiff Kirwan (Marcus Longridge)
• Jonathan Pryce (David Cartwright)
• Hugo Weaving (Frank Harkness)
• Joanna Scanlan (Moira Tregorian)
• Ruth Bradley (Emma Flyte)
• Tom Brooke (JK Coe)
• James Callis (Claude Whelan)