April '56. The first visit of the Kremlin leadership to the West, to England, after Stalin's death. In the company of Nikita Khrushchev and Nikolai Bulganin are the father of the Soviet atomic bomb, academician Igor Kurchatov, and the creator of the country's strategic aviation, Andrei Tupolev. The KGB receives intelligence information about the upcoming secret operation of British intelligence MI6 during the visit. It involves British “frog people” - combat swimmers. The security services are on alert. The chief of Lubyanka, General Ivan Serov, leaves for England. What does April '56 have in store for all of them? The narrative is based on materials collected in the archives of different countries, memories of eyewitnesses, interviews with veterans of special services, as well as direct participants in the historical events described in the book.