‘Slow Horses’ Season 6 Trailer Reveals Olivia Cooke’s Long-Awaited Return as Sid

‘Slow Horses‘ has built its reputation on turning MI5’s biggest screwups into some of television’s most gripping spy storytelling. Across five seasons, Apple TV’s award-winning drama has consistently found new ways to put Gary Oldman’s foul-mouthed Jackson Lamb and his ragtag Slough House crew through the wringer.

That pattern looks set to continue in dramatic fashion with Season 6, which finds the entire Slough House team suddenly hunted by unknown forces. A newly released trailer offers the clearest look yet at just how personal and dangerous this next chapter is about to get for Lamb’s team of disgraced agents.

The trailer’s biggest surprise, though, comes buried near its final moments. Olivia Cooke is set to return as Sidonie “Sid” Baker, the former MI5 operative believed dead since Season 1, marking a comeback fans have speculated about for years.

Sid was shot and left in critical condition back in the show’s first season, with Diana Taverner later telling Lamb that she had died from her injuries. That explanation never fully satisfied longtime viewers, especially after the Season 1 finale revealed River discovered Sid’s MI5 records had mysteriously been erased entirely, hinting she might still be alive somewhere off the grid.

Since her exit from the series, Cooke has gone on to become one of the biggest names on television, currently starring as Alicent Hightower in HBO’s ‘House of the Dragon.’ Her return to ‘Slow Horses’ marks a significant full-circle moment for a character whose fate has lingered as one of the show’s most enduring mysteries.

According to the official logline, Season 6 finds the Slow Horses forced on the run after Diana Taverner, played by Kristin Scott Thomas, drags them into what’s described as a fatally high-stakes game of retaliation and revenge. The trailer opens with Lamb confronting Taverner directly, demanding answers about why members of his team keep turning up dead.

Catherine Standish, played by Saskia Reeves, warns in the trailer that anyone who has ever worked at Slough House is now being targeted, setting the stage for a season built around paranoia and survival. Lamb’s blunt assessment of the unfolding situation, delivered in typically brutal fashion, sums up the stakes bluntly: “It’s a blood bath.”

Season 6 adapts material from both Mick Herron’s fifth and sixth Slough House novels, ‘Joe Country’ and ‘Slough House,’ giving the season a denser narrative foundation than some of the show’s previous outings. Adam Randall returns to direct, having also helmed the show’s fifth season.

Cooke’s comeback isn’t the only reunion teased in the trailer. Rosalind Eleazar returns as Louisa Guy, while Joanna Scanlan reprises her role as the insufferable Moira, both familiar faces from the show’s earlier seasons making their way back into the fold as the team scrambles to warn former colleagues of the danger closing in around them.

The returning cast also includes Jack Lowden as River Cartwright, Christopher Chung as Roddy Ho, and Jonathan Pryce as River’s grandfather David Cartwright, rounding out the ensemble that’s helped make ‘Slow Horses’ one of Apple TV’s most consistently praised original series.

‘Slow Horses’ Season 6 premieres September 16 on Apple TV, with new episodes rolling out weekly through October 21. Given how central Sid’s mysterious fate has remained to the show’s larger mythology, her return alone promises to reshape the emotional stakes for Lamb’s team heading into the new season.

Have something to add? Let us know in the comments!