Along with the trailer release the streamer has announced the return of Olivia Cooke

Gary Oldman’s irascible spy boss Jackson Lamb is trying to get to the bottom of who’s killing off his Slough House agents in Apple TV’s new trailer for season six of Slow Horses — even if he thinks they’re all worthless.

Along with the trailer release, the streamer has announced the return of Olivia Cooke (House of the Dragon, Ready Player One) as Sid Baker, an agent who was believed to have died back in season one.

Slow Horses season six premieres Wednesday, Sept. 16, with one episode dropping each week through Oct. 21. The trailer (which you can watch below) starts with Oldman comically antagonizing his boss, MI5 First Desk Diana Taverner (Kristin Scott Thomas), before asking her if she knows why current and former members of his Slough House division keep showing up dead.

The team then starts to investigate, piecing together that they’re being targeted. “It’s a bloodbath,” Lamb says.

Everyone who’s connected to Slough House is rounded up at a safe house and told to go off the grid, including Louisa (Rosalind Eleazar), who previously said that she intended to quit after she went on a mental health break in season five.

“Stay dark,” Lamb admonishes them. “No phones.” But the order is seemingly ignored

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Hugo Weaving’s Frank Harkness, the nefarious birth father of agent River Cartwright (Jack Lowdon), also makes an appearance, and the trailer previews plenty of explosions, shootouts and even hand-to-hand combat.

It’s not clear who’s behind the chaos, but Apple describes the season this way: “Season six sees the Slow Horses on the run as Diana Taverner embroils them all in a fatally high-stakes game of retaliation and revenge.”

At the end of the trailer, Lamb tells his assistant, Catherine Standish (Saskia Reeves), “Oh come on, we’re spies. We’ve all faked our death at one time or another.” It then cuts to River coming face-to-face with Sid, who was shot in the head in the first season while they were investigating a case together.

After being shot, Sid — a talented spy who had previously confessed to River that Taverner sent her to Slough House to keep an eye on him — was taken to the hospital and spent time in intensive care before the Slough House team was told that she’d died. However, Roddy discovered in the season one finale that Sid’s MI5 records had been erased, which suggested she may be alive after all.

The Emmy- and BAFTA-winning show is based on Mick Herron’s Slough House book series, with this season adapting both the fifth and sixth novels, Joe Country and Slough House.

See-Saw Films produces Slow Horses for Apple TV, with Jamie Laurenson, Hakan Kousetta, Julian Stevens, Iain Canning, Emile Sherman, Adam Randall, Gail Mutrux, Douglas Urbanski and Oldman serving as executive producers. Season six is adapted for television Adam Randall returns to direct.