The Second Vatican Council is the single most influential event in the twentieth-century history of the Catholic Church. The book analyzes the relationship between the Council and the "e;Ostpolitik"e; of the Vatican through the history of the Hungarian presence at Vatican II. Pope John XXIII, elected in 1958, was a catalyst. He thought that his most urgent task was to renew contacts with the Church behind the iron curtain. Hungary, too, did not consider Vatican II primarily an ecclesiastical event. It was considered a component of the negotiations between the Holy See and the Kadar regime: Hungarian participation at the Council was made possible by the new pragmatic attitude in Hungarian church politics. After the crushing of the 1956 Revolution, churches in Hungary thought that the regime would last and were willing to compromise. During the Council Hungary became the experimental laboratory of the Vatican's new eastern policy. Fejerdy tries to establish whether it was it a Vatican decision or a Soviet instruction.