In Slow Horses Season 5, the dysfunctional MI5 team from Slough House faces a new and dangerous crisis against a backdrop of political tension in London. The season opens with a shocking mass shooting in Abbotsfield, which coincides with a heated mayoral race. Some agents suspect that one of their own may have been the target, raising fear that MI5 is being manipulated from within.

Jackson Lamb continues to preside over his ragtag team with his usual gruff humor and cynical brilliance, but this season leans lighter compared to previous entries. Roddy Ho, the tech-savvy but socially awkward “Slow Horse,” becomes a central figure when he unexpectedly gets a girlfriend, triggering both comedic chaos and deeper intrigue. His romantic life draws attention, but it also leads him into dangerous territory that could threaten him and the rest of Slough House.

Meanwhile, tensions within MI5 and Slough House intensify. Deputy Director General Diana Taverner’s ambition grows more ruthless as political maneuvering overlaps with the terror crisis.  She juggles power plays while the Slough House agents scramble to uncover the full scale of the destabilization campaign. As the team pieces together clues, they realize that the attacks, sabotage, and cyber threats may not be isolated incidents—but part of a coordinated effort to shake the foundations of British intelligence.

River Cartwright is also tested emotionally and professionally. Haunted by past betrayals and recent losses, he must confront danger head-on while trying to prove his value. His relationship with Louisa Guy is strained, even as the stakes around them grow higher. As Slough House dives deeper into covert operations, loyalty and trust are pushed to the brink.

Lamb, ever unpredictable, plays his cards close to his chest. He uncovers compromising information that could give him leverage over the MI5 leadership. In a clever counterplay, he forces powerful figures to respond to his demands to protect his team. The season finale reveals major power shifts within MI5, including unexpected resignations and promotions, with Slough House barely avoiding closure.

Underneath the spy plots, Season 5 also explores deeper personal themes. Roddy’s growth, his relationship, and his new vulnerability humanize him in ways that contrast sharply with Slough House’s usual dysfunction. At the same time, Lamb reveals a more vulnerable side, hinting at past trauma and scars that few have seen before.

By the end of the season, the immediate threat is neutralized, but the damage is not without cost. Slough House survives, albeit shaken, and the agents—each flawed and stubborn—come away with a renewed sense of purpose. The finale sets up a tense future, leaving viewers wondering who’ll survive and how the shifting power dynamics within MI5 will play out next.