Now the slow horses have a chance at redemption. An old Cold War-era spy is found dead on a bus outside Oxford, far from his usual haunts. The despicable, irascible Jackson Lamb is convinced Dickie Bow was murdered. As the agents dig into their fallen comrade's circumstances, they uncover a shadowy tangle of ancient Cold War secrets that seem to lead back to a man named Alexander Popov, who is either a Soviet bogeyman or the most dangerous man in the world. How many more people will have to die to keep those secrets buried?