Olivia Cooke’s Sid Baker Makes a Stunning Return in Slow Horses Season 6

One of Slow Horses’ longest-running mysteries is finally moving back into the spotlight. Apple TV has confirmed that Olivia Cooke will reprise her role as Sid Baker in season six, bringing back a character whose fate has remained unresolved since the espionage drama’s first season.

The new season will also see Sir Gary Oldman return as Jackson Lamb, the abrasive head of Slough House and its group of sidelined MI5 agents. Season six premieres on Wednesday, September 16, with episodes released weekly through October 21.

A newly released trailer provides the first glimpse of what awaits the team — and saves its biggest surprise for the closing moments.

A Familiar Face Returns to Slough House

Sid Baker was introduced during the first season and appeared to die after being shot in the head. However, the series never completely closed the door on her survival.

That uncertainty grew when Roddy Ho later discovered that Sid’s records had mysteriously disappeared. The unexplained development left viewers with the possibility that there was considerably more to her story.

Season six has now provided the answer fans have been waiting for.

Near the end of the new trailer, River Cartwright is visibly stunned when he sees Sid standing at the top of a staircase. Olivia Cooke’s appearance confirms that the character is returning, although exactly what happened to Sid — and where she has been — remains unclear.

Given the circumstances surrounding her disappearance, her comeback could become one of the season’s most significant storylines.

The Slow Horses Become the Targets

Sid’s return is not the only problem facing Jackson Lamb and his team.

The trailer shows Slough House confronting a dangerous new threat as members of the group appear to be targeted one after another. Two unidentified attackers, portrayed by MyAnna Buring and Kyle Soller, appear to be connected to the violence.

The official synopsis places the Slow Horses in a deadly cycle of retaliation and revenge, with MI5 figure Diana Taverner becoming caught up in the escalating situation.

Season six draws its story from Joe Country and Slough House, the sixth and seventh novels in Mick Herron’s acclaimed Slough House book series.

Season Five Will Have Consequences

The new chapter will also build directly on developments from season five.

Christopher Chung, who plays technology specialist Roddy Ho, previously indicated that there would be substantial crossover between the two seasons. One particularly important change involves Diana Taverner, played by Kristin Scott Thomas, following her promotion to First Desk.

That new position could significantly alter the dynamics inside MI5 as the Slough House team attempts to understand who is targeting them and why.

With Sid unexpectedly returning at the same time, season six has several unresolved threads from earlier episodes ready to collide.

Who Is Returning for Season Six?

Gary Oldman once again leads the ensemble as Jackson Lamb, while Kristin Scott Thomas returns as Diana Taverner and Jack Lowden reprises his role as River Cartwright.

Saskia Reeves, Christopher Chung, Aimee-Ffion Edwards, Rosalind Eleazar, Joanna Scanlan, Samuel West, Ruth Bradley, Tom Brooke, Jonathan Pryce and Hugo Weaving are also returning.

BAFTA winner Lenny Rush joins the cast for the new season, alongside MyAnna Buring and Kyle Soller.

But for longtime viewers, Olivia Cooke’s return as Sid Baker may be the addition that raises the biggest questions.

Her apparent death helped shape the show’s first season, while the later disappearance of her records suggested that her story might not be finished. Now that Sid has resurfaced, season six finally has the opportunity to reveal what really happened.

When Does Slow Horses Season 6 Premiere?

Slow Horses season six premieres Wednesday, September 16.

The first episode will arrive that day, followed by one new episode each week until October 21.

With Slough House under attack, Diana Taverner occupying a powerful new position and Sid Baker suddenly back after years of uncertainty, the sixth season is bringing one of the series’ earliest mysteries directly into its newest crisis.