Slow Horses season 6 trailer confirms Olivia Cooke return at long last

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It’s only taken four seasons, but Olivia Cooke is finally returning to the Slow Horses fold.

Hot off the presses, the trailer for season six shows scene-stealer Sid has risen from the dead (yes, we all knew she didn’t really die).

Like clockwork, the Apple TV hit will be back on screens this September and this first look makes it clear that our gang of loser spies are under shadowy attack.

Gary Oldman’s Jackson Lamb asks Diana Taverner (Kristen Scott Thomas), having snuck into her garden, ‘Do you know anything about why my Slow Horses keep turning up dead?’

We then see a couple of grisly fates: one spy shoved from a canal boat, another locked in a flaming shipping container. Later on, Moira (Joanna Scanlan) is sprayed in the face with something that probably isn’t water, by figures wearing gas masks.

There’s a list, we’re told, of all the employees past and present of Slough House. Otherwise known as a kill list.

Olivia Cooke in the Slow Horses trailer
The trailer for season six shows scene-stealer Sid has risen from the dead (Picture: Apple TV/YouTube)
Jack Lowden and Sir Gary Oldman in "Slow Horses," premiering 16 September 2026 on Apple TV.
The Slow Horses are back up to no good this September (Picture: Jack English/Apple TV)
Comment nowAre you excited to watch Slow Horses season 6? Have your say below!Comment Now

As a result, it isn’t just Cooke back this season, because the gang also go looking for Louisa (Rosalind Eleazar) to warn her, after she quit MI5 the season before last. 

The Slow Horses are sent to a safe house, told to stay off their phones (naturally, Roddy immediately breaks this rule) as Lamb declares it ‘a bloodbath!’ 

River’s shady American father (Hugo Weaving) might somehow be involved, because he’s back in the picture. 

Then, Lamb imparts Catherine (Saskia Reeves) with some more words of his maybe-wisdom: ‘We’re spies. We’ve all faked our death at one time or another.’

After which, a weary-looking River climbs a set of stairs only to see Cooke’s Sid, clad in a heavy coat, waiting at the top for him.

What Sid’s return means for Slow Horses

Good things!

Olivia Cooke’s Sid Baker was the only one with any know-how in the Slough House building during season one. Taverner called her the ‘most capable’ of the Slow Horses.

Competency porn is its own TV phenom at the moment (thank you, The Pitt) and Sid was a stellar example of it; someone who knows how to do their job incredibly well, making for a satisfying watch.

All the more enjoyable when she lorded it over Lowden’s River, who was more of an eager all-the-gear, no-idea type of spy back then (and sometimes still now). The pair also had the flickerings of romance, which their brief exchange in the trailer doesn’t discount is still there.

Given that Lowden then had a spot of some sort of chemistry with Louisa, who is also back this season and may well end up in the safe house with the two of them, the six-parter is ripe for theatrics. Roll on September.

'Best spy thriller on TV' confirms season 6 plot ? and it's back very soon Slow Horses picture: Apple
Diana Taverner (Kristen Scott Thomas) might know why the Slow Horses are being targeted… (Picture: Courtesy of Apple)
Lenny Rush and Christopher Chung in "Slow Horses," premiering 16 September 2026 on Apple TV.
Lenny Rush is joining the show as newcomer Morris, while Christopher Chung is back as tech whizz Roddy Ho (Picture: Jack English/Apple TV)

The same year that she burst onto screens with a starring role in House of the Dragon, Cooke played the one decent, dry-witted spy in Slough House. 

Because it made no sense why Sid had landed in the reject’s palace, it soon emerged that she had been sent there to keep an eye on Lowden’s River, after an epic Stansted screw-up, which kicked off the show. 

The short but sweet turn ended in a bloody fashion, with Sid shot in the head and (off-screen) declared dead…except that looked less likely once the Slow Horses realised all evidence of her ever having existed had been scrubbed. 

Slow Horses fans have long wondered if and when Sid would be back – and the answer is September 16, when the sixth series premieres, adapted from the sixth and seventh novels in Mick Herron’s Slough House series. 

Slow Horses season six premieres on Wednesday, September 16, with the first episode, followed by one episode weekly until October 21.

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