The introduction is a flash-forward scene that took place on May 18, 1985. Operatives of the KGB—the Soviet Union’s state police and intelligence arm—entered a Moscow apartment to plant bugs, video cameras, and even radioactive dust—enough to set off a reading on a Geiger counter but not enough to harm someone. The apartment, in a complex of buildings where KGB officers lived, belonged to Colonel Oleg Antonyevich Gordievsky, who had just been promoted to KGB chief in London. Gordievsky arrived from London a few hours later, returning to Moscow to have his new position formally conferred from the head of the KGB.

Gordievsky was secretly a British spy. The British foreign intelligence service MI6 had recruited him over a decade earlier, and given that he’d now lead the KGB in Britain, MI6 would know in advance everything the Soviets planned to do. As Gordievsky made his way through the airport, he sensed a stronger KGB presence than usual: More plainclothes officers were in surveillance, and the processing of his passport seemed to take longer. Gordievsky and MI6 had considered the possibility that his invitation to Moscow was a trap and had devised an emergency escape plan, code-named PIMLICO, just in case.