Bad Actors

The story opens with Anthony Sparrow, the Prime Minister's special adviser, hiding in a foxhole during an organized brawl between English and Italian football hooligans known as Ultras. While casually advising a caller on political strategy, Sparrow clubs a man who stumbles into his clearing, then beats him even after realizing the man is on his own side. His call ends with "Yes, prime minister," establishing the link between Downing Street and organized thugs.

The narrative introduces Slough House, the decrepit London building where MI5 banishes its disgraced agents, the "slow horses," under Jackson Lamb, a slovenly veteran spook. The roster includes Louisa Guy, who keeps her combat skills sharp on a department-store dummy; Lech Wicinski, an exiled analyst whose face bears self-inflicted scars hiding an obscenity an enemy carved into his skin; Roderick Ho, the team's tech specialist; and Ashley Khan, the newest member, who resents Lamb for breaking her arm during their first encounter. Shirley Dander, who has a cocaine addiction, has been placed in the San, a Service rehabilitation facility in Dorset, through the intervention of Catherine Standish, Lamb's administrative assistant who is in recovery from alcohol addiction. Catherine manages daily operations while Lamb assigns pointless busywork designed to bore his staff into quitting.

The central plot concerns Dr. Sophie de Greer, a Swiss academic and "superforecaster" reputed to predict electoral responses with unusual accuracy, who works on Sparrow's advisory group. She has been missing for three days. Oliver Nash, chair of the Limitations Committee (the body overseeing MI5's budget), asks Claude Whelan, a former First Desk (MI5's chief), to investigate at Sparrow's urging. Sparrow suspects MI5 used an illegal Cold War-era protocol called Waterproof, a form of secret rendition, to make de Greer disappear. Whelan is reluctant but agrees, partly from lingering resentment toward current First Desk Diana Taverner and Lamb, who engineered his removal from office.

Whelan visits Taverner at Regent's Park, MI5's headquarters. She dismisses the investigation as a Sparrow power play aimed at bringing the Park under Downing Street control and provides phone records. However, she has secretly had Josie, a hub staffer, plant a fabricated call from de Greer's mobile to a Park phone number, intending to send Whelan on a wild-goose chase. Whelan discovers the call, dials the number, and disconnects without speaking, shaken by the connection.

At a Russian Embassy reception, Taverner discovers that Vassily Rasnokov, Moscow's First Desk and a senior GRU officer, has been in London for two days under an alias, undetected by the Park. Rasnokov reveals that he dined with Sparrow in Moscow the previous month, a contact Sparrow never reported, and mentions de Greer by name before departing.

The novel's structure is nonlinear. At a park bench meeting, Lamb tells Taverner the backstory in a flashback. Days earlier, John Bachelor, a Service "milkman" (a caretaker for retired agents), told Lech he recognized a woman on TV as the living image of Colonel Alexa Chaikovskaya, a KGB officer he had observed in Bonn in 1988. The woman was de Greer; Bachelor believes she is Chaikovskaya's daughter. Lech and Louisa trick Roddy into retrieving an archive photograph that confirms the resemblance, then drive to Wimbledon to surveil de Greer's apartment. When de Greer goes for an evening run, Louisa follows on foot and spots two men closing in: Italian Ultras sent by Sparrow through Alessandro Botigliani, known as "Benito," a leader of the Ultras. Louisa intervenes, and de Greer returns with a brick to free her from one attacker. Shirley, who has tracked them using a phone app, arrives separately and is arrested after smashing a tourist coach's windscreen. Afterward, de Greer agrees to come in, and Lamb stashes her at a Chelsea safe house secretly provided by Peter Judd, a former politician tied to a clandestine funding cabal, with Bachelor as babysitter.

At the safe house, Lamb interrogates de Greer and establishes that Rasnokov planted her to stoke conflict between Sparrow and the Park. Her superforecasting credentials were fabricated; her real role was to reinforce Sparrow's policy instincts while giving Moscow leverage. When pressed, de Greer reveals the scheme was her mother's: Colonel Chaikovskaya remains Rasnokov's handler. Lamb also notes that two bottles of The Balvenie whisky Rasnokov ordered at his hotel have vanished.

Events accelerate when Sparrow plants the word "waterproof" in a Times article linking de Greer's disappearance to the Service, then pressures Nash to convene an emergency Limitations Committee meeting. His goal is to remove Taverner and install a compliant successor, effectively bringing the Park under Downing Street control. He directs Benito's Ultras to attack the San, believing de Greer is held there under Shirley's name.

Taverner, warned by a whispered phone call invoking the Candlestub Protocol (the Service's suspension procedure), dumps her phone and goes on the run through London. The Dogs, MI5's internal police, track her to a bar on Cheapside, where Judd has arranged cash. Lamb sends Louisa and Lech to help. In the ensuing chaos, Taverner overpowers a Dog officer, seizes the woman's gun, and commandeers the Dogs' SUV to escape.

At Slough House, Roddy and Ashley trace Rasnokov's movements. Ashley reveals that her unfinished training paper covered Rasnokov's early career, including his teenage nickname, "The Fireman," earned by starting fires as a debt collector. Roddy connects this to a fatal house fire near the Westway, where arson investigators found two glass bottles in the wreckage. The missing Balvenie bottles tie Rasnokov to the fire and to an escape plan: The dead man was an "understudy" whose fabricated identity Rasnokov intends to assume after faking his own death.

At the San, the Ultras' raid unfolds violently. Shirley triggers the fire alarm and, alongside fellow patients, fights off invaders on an upper landing. Whelan, who has driven to Dorset expecting to find de Greer, arrives mid-raid. Shirley is knocked unconscious and loaded into a people carrier, but Whelan leaps onto its roof from a staircase and batters the windscreen with a baseball bat until a police helicopter's searchlight halts the vehicle.

In the predawn hours, de Greer slips away from the safe house with Bachelor. When Taverner reaches the safe house, she finds Lamb alone. He explains that exposing de Greer before the Limitations Committee would reveal the understudy scheme and get Rasnokov killed. Instead, the Park should let de Greer walk and allow Rasnokov to step into his new identity. Once he does, the Park can locate and "own" him, gaining access to his secrets while Moscow believes he is dead.

De Greer, meanwhile, makes two phone calls: one to Sparrow, offering to deny being a plant in exchange for a lobbying job, and another to Benito, predicting exactly what Sparrow will promise and threaten. When Sparrow meets de Greer and Benito at a café, de Greer exits and Sparrow finds himself trapped between Benito's enforcers. Benito chose de Greer's offer, the Park's help with his crew's legal troubles, over Sparrow's empty promises. The Ultras drive Sparrow to their fighting woods.

That morning, Taverner visits Nash, who reveals he warned her and discovered the Sparrow-Benito connection himself. At the Limitations Committee meeting, no case is presented: De Greer has made a brief online appearance apologizing for missing work, and Sparrow fails to appear. Taverner is reinstated to a standing ovation at the Park.

The final chapter surveys the aftermath. Rasnokov reportedly dies in a boating accident on the Barents Sea; no body is recovered. The Park secretly establishes "Operation Rosebud" to watch for whoever steps into the understudy's identity. Sparrow cowers in the woods, hunted by the Ultras. Shirley returns to the San at Catherine's insistence, acknowledging for the first time that she is not fine. Bachelor vanishes, surfacing only in a rambling late-night call to Lech. Lamb sits alone in his darkened office, contemplating Rasnokov's possible future, as Slough House settles back into its usual stupor.