From two of the world’s leading intelligence and espionage historians comes the definitive—and most unsettling—account of the assassination of Leon Trotsky. Exiled from the Soviet Union and living under constant threat, Leon Trotsky believed that by 1937 he had found sanctuary in Mexico City. What he did not see was the vast clandestine machinery Stalin had already set in motion—one that beyond Europe and, crucially, into the United States itself. Drawing on newly uncovered evidence, this book reveals the previously untold role played by Stalin’s agents operating in America who helped make the assassination possible. At the center of the plot stood Ramón Mercader, a disciplined Soviet assassin using multiple false identities. Guided by his formidable mother, Caridad Mercader, he avoided overt violence in favor of patience, manipulation, and emotional infiltration. His most powerful weapon was not the ice axe he ultimately wielded, but trust—carefully cultivated through friendships, sympathies, and a romantic relationship with Sylvia Ageloff, a Brooklyn-born social worker whose true role in the assassination is reassessed here with startling clarity. Based on unprecedented access to classified documents in Mexico, the United States, and Russia, as well as unpublished correspondence from Trotsky’s personal guards, Nigel West and H. Keith Melton expose the fatal blind spots in Trotsky’s own security and thinking. His lifelong faith in personal loyalty, his dismissal of internal betrayal, and a measure of revolutionary hubris proved decisive in the final hours of his life. More than merely the story of how Leon Trotsky was murdered, this is a sweeping history of espionage, ideology, love, betrayal, and fatal miscalculation; it is the complete, never-before-told account of an assassination that changed the course of modern history.