Director: Saul Metzstein
Executive Producers: Graham Yost, Will Smith, James Hawes, and others
Age Rating: TV-MA (US)
Series Debut: April 1, 2022
Two novels adapted: Season 6 draws from both Joe Country and Slough House, the sixth and seventh books in Mick Herron’s espionage series
Status: Renewed for Seasons 7 and 8

Old Enemies and New Threats

The sixth season of Slow Horses premiered on Apple TV on September 16, 2026, bringing another six episodes of espionage, betrayal, and political intrigue. The story finds Jackson Lamb and his disgraced MI5 operatives caught in a dangerous campaign of retaliation, as a series of suspicious deaths and the return of former CIA operative Frank Harkness place the team in jeopardy.

As the investigation unfolds, familiar faces resurface and loyalties become increasingly uncertain. River Cartwright faces personal complications involving his family and former colleague Sid Baker, while the threat against Slough House grows into a wider intelligence crisis.

Jackson Lamb and His Misfit Agents

Gary Oldman returns as Jackson Lamb, the abrasive, perpetually disheveled intelligence veteran whose unconventional leadership continues to define the series. His sharp instincts and merciless insults remain central to the team’s survival, particularly as his agents face threats that expose their individual vulnerabilities.

Jack Lowden’s River Cartwright takes on a prominent role alongside returning characters Catherine Standish, Louisa Guy, Roddy Ho, Shirley Dander, and J.K. Coe. The unexpected return of Sid Baker adds another dimension to the group’s complicated relationships, bringing unresolved personal history into an already dangerous situation.

Revenge Runs Through MI5

_{Kristin Scott Thomas as Diana Taverner}

Season 6 explores the consequences of covert intelligence operations through a series of assassinations, hidden alliances, and dangerous attempts to settle old scores. Diana Taverner, played by Kristin Scott Thomas, becomes increasingly entangled in the crisis as her efforts to maintain control of MI5 collide with the investigation unfolding at Slough House.

The return of Frank Harkness introduces further complications, particularly through his connection to River Cartwright. Political self-preservation, institutional secrecy, and competing intelligence interests shape a conspiracy in which even experienced operatives struggle to distinguish allies from enemies.

Action and Insults Keep Coming

The series’ trademark dark humor remains a defining feature of Season 6, with Jackson Lamb’s insults and the team’s dysfunctional relationships providing a steady stream of uncomfortable comedy. The writing continues to find humor in bureaucratic incompetence, bruised egos, and the absurdities of intelligence work.

Director Adam Randall maintains the show’s brisk pacing through escalating confrontations, tense pursuits, and sudden bursts of violence. The combination of sharp dialogue, unpredictable action, and morally compromised characters preserves the cynical atmosphere that has distinguished Slow Horses throughout its run.

Old Enemies and New Threats

Jackson Lamb and His Misfit Agents

Revenge Runs Through MI5

Action and Insults Keep Coming

Season 6 Character Highlights