More than a century ago, the new Bolshevik government began sending Soviet citizens abroad as deep-cover spies, training them to pose as foreign aristocrats, merchants, and students. Over time, this grew into the most ambitious espionage program in history. Many intelligence agencies use undercover operatives, but the KGB was the only one to go to such lengths, spending years training its spies in language and etiquette, and sending them abroad on missions that could last for decades. These spies were known as "illegals." During the Second World War, illegals were dispatched behind enemy lines to assassinate high-ranking Nazis. Later, in the Cold War, they were sent to assimilate and lie low as sleepers in the West. The greatest among them performed remarkable feats, while many others failed in their missions or cracked under the strain of living a double life.

Drawing on hundreds of hours of interviews, as well as archival research in more than a dozen countries, Shaun Walker brings this history to life in a page-turning tour de force that takes us into the heart of the KGB's most secretive program. A riveting spy drama peopled with richly drawn characters, The Illegals also uncovers a hidden thread in the story of Russia itself. As Putin extols Soviet achievements and the KGB's espionage prowess, and Moscow continues to infiltrate illegals across the globe, this timely narrative shines new light on the long arc of the Soviet experiment, its messy aftermath, and its influence on our world at large.