Dead Lions is a 2013 spy novel by Mick Herron. The novel is the second in the Slough House series, which follows a group of British intelligence misfits known as the “slow horses,” who are exiled to Slough House after failing at MI5. Dead Lions explores the legacy of the Cold War in a changing 21st-century Great Britain. As with the other novels in the Slough House series, the novel was adapted for television. 

This guide uses the 2017 John Murray edition of Dead Lions.

Content Warning: The source text and this guide mention alcohol and substance use disorder, suicide, and terrorist acts.

Plot Summary

Dead Lions begins with the death of a washed-up M15 agent named Dickie Bow. Dickie died on a bus while pursuing a man he recognized through London, but he left a message for his former colleagues. Though his death is initially deemed natural, Jackson Lamb, the head of Slough House and a former Cold War spy, suspects foul play. Lamb’s curiosity is piqued because Dickie, though past his prime, was a field agent during the Cold War. Lamb does not believe that Dickie simply died.

Lamb begins investigating Dickie’s death and discovers that before he died, Dickie tailed a mysterious bald man. Despite the lack of official interest, Lamb brings the matter to his team at Slough House, the central base for the “slow horses,” a ragtag group of agents who are mostly disgraced. The slow horses include Catherine Standish, a former secretary who has an alcohol use disorder; River Cartwright, a young agent with a strong sense of duty who failed a training exercise; Louisa Guy, a jaded agent trying to keep her career afloat amid a romantic relationship with her colleague, Min Harper; and Roderick “Ho” Ho. Two new team members are introduced: Shirley and Marcus. Lamb assigns them tasks to help uncover the truth about Dickie’s death.

As Lamb digs deeper, he learns that Dickie’s death may be linked to a forgotten Cold War espionage operation called Cicadas, which involved sleeper agents placed in Britain. Like cicada insects, these Cicada agents were intended to wake up after a long period of dormancy. Lamb suspects that Cicada agents were reactivated, meaning that a covert Russian operation is underway. Min and Louisa are sent to Regent’s Park to assist with a meeting set up by James Webb, an M15 agent. The meeting aims to recruit a mysterious Russian oligarch named Arkady Pashkin as a British intelligence asset. Louisa and Min investigate Pashkin’s security team while Webb is forced to reveal his ploy to Diana Taverner, his superior.

Lamb sends River to a small town called Upshott, which is located near a former American military base. The British Ministry of Defense now operates it, and the town hosts a quiet community of middle-class retirees and their children. Meanwhile, Min has a small quarrel with Louisa, prompting him to investigate Pashkin’s security guards. Min is caught, and after he catches a passing glimpse of an unnamed man, he is killed. 

In Upshott, River spends three weeks undercover investigating the local people. They are all unremarkable, though he develops a romantic relationship with Kelly, whose parents moved to Upshott when she was very young. She is a member of the local flying club and spends her afternoons piloting a small plane. Meanwhile, Louisa mourns Min’s death by sticking to the Pashkin assignment. She works with Marcus, who is worried about her. Louisa is convinced that Pashkin knows something about Min’s death; she goes on a date with him, but Marcus intervenes before she can execute her plan to torture Pashkin.

In Slough House, Lamb seems aware that the death of Dickie Bow was meant to capture his attention. He remembers an old legend about a Russian spymaster named Popov. Catherine and Ho find information to support Lamb’s theory that many of the residents of Upshott are Russian sleeper agents, the Cicadas. Lamb tracks down an elderly, low-ranking former Soviet spy who now lives in London. The man is dying, and he believes that this Katinsky may be Popov, who is now activating his sleeper agents.

River is lured to the Ministry of Defense base by a local who resents his relationship with Kelly and hoped he will get hurt. River is found by another local named Tommy Moult, who takes him back to the flying club. There, River catches sight of materials that could be used to make a bomb. He debates whether he should call this in, but Moult attacks him before he can decide. After another altercation, River contacts Catherine and warns her that Kelly may be flying a small plane to London, armed with a bomb.

The meeting between Webb and Pashkin occurs on the same day as a political march in London. Louisa and Marcus escort Pashkin and his team to the meeting. During the conversation with Webb, Pashkin pulls out a gun. He shoots Webb as River’s warning about the plane causes the building to lock down. The building is evacuated while the protest outside turns into a riot. This provides Pashkin with the cover needed to steal diamonds from a dealer in the skyscraper. Meanwhile, Catherine and Ho discover that Pashkin’s identity is false. He is not really a billionaire. Louisa and Marcus try to stop Pashkin as Kelly’s plane heads toward London. Louisa confronts Pashkin on the roof, where Marcus shoots him, spilling the diamonds everywhere.

In Upshott, River comes to believe that the bomb on the plane was a fake and that Kelly is planning to drop political leaflets on the marchers. Her plane is intercepted and led away before it can cause any damage. River tracks down Tommy Moult, who is revealed to be the Russian spy, Katinsky. Katinsky explains that a British scheme destroyed his hometown. He has been working with Pashkin, but he does not care about the diamonds. He is dying of cancer, and he wants revenge. However, when Katinsky tries to detonate the bombs planted by the Cicadas, nothing happens. The Cicadas, as River suspected, did not want to betray their assumed identities. Instead, Katinsky blows himself up. 

At Slough House, the inhabitants settle back into their familiar routine. Still pained by grief, Louisa tells no one about the diamond she picked up on the rooftop, which she has hidden on her person.