Slough House

Mick Herron’s 2021 spy thriller, Slough House, is the seventh volume in his acclaimed series of the same name. The novel continues the story of a team of disgraced MI5 agents relegated to Slough House, a dilapidated administrative outpost. Nicknamed the slow horses, the teams discovers that their personnel files have been mysteriously erased from the official database. They soon find themselves targeted by a Russian assassination squad using an outdated roster. The agents must navigate a dizzying web of betrayal within their own agency and the corrupt political sphere to survive. The novel explores themes including Bureaucratic Indifference to Human Life, The Manipulation of Populist Outrage, and The Need for Solidarity Among Outcasts.

The plot of Slough House is directly inspired by contemporary events, including the 2018 Salisbury Novichok poisonings and the rise of populist street movements like the Yellow Vests in the UK. Herron, often regarded as a satirical successor to John le Carré, uses these real-world touchstones to examine the cynical intersection of politics, media, and modern espionage. The novel was a Sunday Times bestseller and won the Theakston Old Peculier Crime Novel of the Year in 2022; it was also nominated for the Barry Award for Best Thriller. The Slough House series has been adapted into the critically acclaimed Apple TV+ show Slow Horses, starring Gary Oldman. Herron is a highly decorated author, having also won the CWA Gold Dagger for Dead Lions and the CWA Diamond Dagger for lifetime achievement.

This guide refers to the 2021 Soho Crime edition.

Content Warning: The source text and guide feature depictions of graphic violence, physical and emotional abuse, substance use, addiction, illness or death, cursing, antigay bias, ableism, and mental illness.

Plot Summary

In a foreign city, a female intelligence agent is assassinated by a woman in grey. The news is delivered to Diana Taverner, the First Desk of Britain’s MI5, who coolly quotes a line from Ian Fleming: “Smiert spionam,” meaning “Death to spies” (4). Back in London, the slow horses—the name given to the disgraced agents exiled to the decrepit administrative outpost of Slough House—discover their personnel files have been mysteriously erased from the official MI5 database. One of the team, Louisa Guy, is tailed through the city by a young agent, whom she identifies as a trainee when his phone and hers both receive a service-wide text alert simultaneously. 

Meanwhile, another slow horse, River Cartwright, receives a call from his late grandfather’s neighbor, Jennifer Knox, reporting intruders in the empty house. River drives to Kent to investigate, where he finds not burglars, but Sidonie “Sid” Baker, a former slow horse he believed had been killed in the line of duty years ago. She has been waiting in his grandfather’s study. Sid explains that she has been living in a protected MI5 cottage in Cumbria after a long recovery from her head wound. Recently, however, she was forced to flee after a man and a woman posing as missionaries came to her door. She is convinced they were assassins sent to kill her. 

Back at Slough House, the foul-tempered chief, Jackson Lamb, deduces that Taverner has wiped their records to use them as anonymous, real-world targets for training new recruits. This theory is complicated when Lamb is approached by Reece Nesmith III, an American man whose journalist partner, Andrey, was recently murdered in Moscow. Reece claims Andrey had uncovered a plot by the Russian GRU—Russia’s primary foreign military intelligence agency—to assassinate a supposed British hit squad in retaliation for a secret, British-backed hit on a GRU agent in Kazan. The situation escalates when Lamb’s administrator, Catherine Standish, learns that two other former slow horses, Kay White and Struan Loy, have recently died in suspicious accidents. Lamb realizes the GRU is acting on Reece’s information and hunting his agents using an old, outdated Slough House roster.

The political machinations behind the Kazan hit are revealed: Taverner, frustrated by budget cuts, accepted off-the-books funding from a group of wealthy patriots assembled by disgraced politician Peter Judd. One of the key funders is Damien Cantor, a young and arrogant media mogul who owns the news channel, Channel Go. Impatient for influence, Cantor had one of his former security men, Tommo Doyle, infiltrate MI5’s internal police force, known as the Dogs. Doyle gained access to the Park’s paper archives, run by the cantankerous Molly Doran, photographed the old Slough House file, and passed it to Cantor, who then leaked it to his Russian contacts. 

In Leicester, the GRU assassins Jim and Jane track down Struan Loy and burn him alive in the shipping container in which he was living. Since they are new recruits, not listed on the outdated roster, two of the slow horses, Shirley Dander and Lech Wicinski, attempt to turn the tables by capturing one of the MI5 trainees who is tailing them. In a public toilet at Old Street station, they accidentally attack and rob a civilian instead.

The assassins, Jim and Jane, learn Sid’s location from the neighbor, Jennifer Knox. They abduct Sid, planning to drown her in a nearby lake. River arrives at his grandfather’s house moments later, discovers Sid is gone, and gets a description of the car from a frantic Mrs. Knox. He gives chase, his reckless driving nearly causing a head-on collision. He finds the assassins’ car parked by the lake and witnesses Jane trying to drown Sid from a wooden jetty. A brutal fight ensues, during which Sid, having concealed a stiletto letter opener belonging to River’s grandfather up her sleeve, stabs Jim through the jaw and kills him in the car. River fights Jane on the jetty and, with Sid’s help, he manages to overpower and drown her in the lake. Shaken and injured, they take the assassins’ car, leaving the bodies inside, and plan to return to the house to call for help.

Having learned of the murders of his former agents, Lamb activates an emergency protocol, summoning the team to the grave of poet William Blake in Bunhill Fields cemetery. To send a direct message to Taverner, he intercepts and breaks the arm of the trainee agent tailing his tech expert, Roddy Ho. Lamb then confronts Taverner, revealing he knows about her private funding and Cantor’s treachery. He informs her that his team has already dealt with the threat; unbeknownst to her, a second GRU hit team has been active, and Lamb’s slow horses—Louisa, Lech, Shirley, and Roddy—have successfully tracked and captured them. Taverner’s own plan to trade safe passage for the assassins in exchange for evidence against Cantor is now moot. 

Lamb dispatches his team to abduct Cantor, who is taken from outside his apartment tower and imprisoned in the empty room above a closed-down Soho tobacconist’s shop. Meanwhile, Peter Judd, in a power play, orchestrates a minor riot at a Yellow Vest protest, which he then has his new political protégé, Desmond Flint, heroically quell on live television.

Taverner confronts Judd, who reveals an even deeper betrayal: A significant portion of his PR firm’s start-up money, which funded the cabal that backed Taverner, came from Chinese sources. He now has her completely compromised. 

Back in Kent, having made it to a layby, River uses his phone to call Lamb and report the assassins are dead. On Lamb’s orders, they return to his grandfather’s house to await pickup. For the first time in years, feeling his old home is truly his, River uses the front door. As he steps inside, he collapses. Sid rushes to his side, realizing he has been poisoned by a nerve agent—Novichok—smeared on the doorknob by the assassins before they captured her. She finds his phone and desperately calls for emergency services. 

In the aftermath, the slow horses are left to process the attack on River. Louisa runs obsessively, Lech bakes bread, Roddy loses himself in video games, and Shirley dances in a nightclub. River’s grandfather’s house is shrouded in canvas and dismantled by a hazmat team. The final image is of a bulky shadow, presumably Lamb, ascending the stairs in the dark and now-empty Slough House, a lone cigarette glowing in the gloom.