Slow Horses Season 5 Ending Explained: What's Next For MI5

Updated Sep 18, 2026, 11:00 AM EDT Zach Moser has been writing for ScreenRant since 2022, covering movies, classic TV, and streaming TV. His areas of expertise cover a wide range of genres with a particular interest in horror and drama, and the conversations around the TV and film industry. When he's not covering the latest film releases or chronicling the latest season of a new show, he's writing humor pieces for McSweeney's Internet Tendency, Slackjaw, and Points In Case or working on short stories and his second novel. Warning! This article contains MAJOR SPOILERS for the Slow Horses season 5 finale. With the close of another season of Slow Horses, things look to be very different for the future of the popular British spy drama series. Slow Horses season 5 was a rollercoaster as the team at Slough House made some of the biggest blunders of their careers before ultimately saving London and MI5 from catastrophic disasters. While season 5 appeared to move at a slower pace and the focus was much narrower this season, with almost all the adventures taking place in a small radius, the finale was compelling. River Cartwright (Jack Lowden) was redeemed for some of his mistakes, Jackson Lamb (Gary Oldman) once again proved why he is an exceptional agent, and MI5 experienced a major shake-up. All of this was folded in with some big twists and surprise reveals that helped to further define these characters and make the story that much richer. In addition, it also did a great job in setting the stage for some exciting new developments in Slow Horses season 6 and beyond. Diana Taverner Takes Over As The Head Of MI5 Credit: Sony Pictures Television Studios via MovieStillsDB Claude Whelan (James Callis) assumed the position of First Desk at MI5 in Slow Horses season 4. Since then, he has proven to be a poor fit for the role, and much of his time was spent trying to deal with personal situations rather than actually running MI5. Meanwhile, Second Desk Diana Taverner (Kristin Scott Thomas), who has spent years in the service, was leading the organization in his stead. This is further exemplified in the finale when Tara (Hiba Bennani), one of the terrorists blackmailing MI5, calls and asks to speak to the person in charge, referring to Diana and dismissing Claude. Later in the episode, this is paid off when Jackson Lamb uses a recording of Claude to secure the future of Slough House and to force Claude to resign. In the aftermath, Diana Taverner has finally assumed the position as MI5 First Desk, which has been an ongoing ambition for the character since the first season. Diana's wealth of experience ensures she can perform to a high level in this role, but there are bound to be new challenges that arise with Taverner in charge. London Is Safe Once Again After A Penetrating Terrorist Attack For much of Slow Horses season 5, the identity of the people causing havoc in London was inconclusive. While the attackers appeared in the first episode, their identity and motivations remained hidden until much later. But episodes 5 and 6 exposed them as being a small group of disgruntled Libyans who previously participated in peaceful protests. Growing weary of the way their country was treated by the British Armed Forces and left to fend for itself, these radicals banded together to enact a revenge plot against Claude Whelan. The hope was to embarrass and expose the Head of MI5 due to his involvement as a consultant who recommended the UK leave Libya due to the costs being too high and without significant returns. In this way, it was a very personal attack, carried out on a large platform, and resulting in dozens of casualties, and even a flock of innocent penguins. Fortunately, Jackson Lamb and his team recognized what was happening in time, and they successfully prevented the assassination of Mayor Jaffrey (Nick Mohammed), and saved Claude Whelan. Jackson Lamb’s Deformed Feet Reveal A Dark Truth About His Past Courtesy: Apple TV+ One of the more surprising reveals in the season 5 finale comes from a rather grotesque close-up shot of Jackson Lamb's foot. Earlier in the season, in episode 3, Slough House manages to break out of the MI5-imposed lockdown when Lamb tells a dark story about a spy who was tortured during a mission in Russia. Lamb recounts how this young spy was being interrogated in an effort to gain classified information, and when he didn't answer his interrogators, even under extreme pain and suffering, they opted for a different method of torture. The interrogators brought in, tortured, and killed a young woman that the spy was romantically involved with, and who was also carrying his child. The story subtly signaled Lamb's team to pull together and use ordinary objects as weapons, but the story also revealed a heartbreaking truth about Lamb's past. When Catherine Standish (Saskia Reeves) asked if he was the spy in the story, Lamb rebuffed the idea, but the burns on his foot reveal that he was the man in that story who witnessed his pregnant partner murdered in front of him. River Cartwright Is Not Going Back To The Park Slow Horses season 5 almost saw River Cartwright regain his place at the Park after he saved the life of Claude Whelan. As First Desk, Whelan had the power to bring Cartwright back, and it appears that this was his intention. However, when Lamb blackmails Whelan to resign, Cartwright's continued future at Slough House is confirmed. Lamb didn't do this to spite Cartwright, but he needed to stop Whelan from shutting down Slough House. And with Diana now in charge, Cartwright is unlikely to ever get back to MI5 HQ, considering the fact that she personally dislikes Cartwright after his earliest stunts in MI5 resulted in Cartwright digging up personal details about Taverner that she would have liked to keep hidden. How Slow Horses S5's Ending Sets Up Season 6 Slow Horses season 5 concludes with a number of things in place to set up the next season. Evidently, the change in leadership will surely play a large role in what comes next for the team at Slough House, but seeing how they played a major role in securing the terrorists and protecting MI5, it would make sense for them to get a little more respect. However, the teaser trailer for season 6 at the end disproves this with the reveal that Slough House has been eradicated from the system, leaving Lamb and his team in their most precarious position to date. Slow Horses season 6 is sure to be a roller coaster, with major changes for the team and MI5 ahead. Release Date April 1, 2022 Network Apple TV+ Showrunner Douglas Urbanski Cast Jack Lowden River Cartwright Directors Adam Randall, James Hawes, Jeremy Lovering, Saul Metzstein Writers Mark Denton, Jonny Stockwood