The book delineates the methods of operation of the Yugoslav secret political police called UDBA (Uprava državne bezbednosti – State Security Administration), the main institution of the Yugoslav communist regime for the surveillance of society in the Socialist Federal Republic of Yugoslavia (SFRY). The UDBA, which was renamed the State Security Service (Služba državne sigurnosti) in 1967, had a different role from that of the security intelligence services in the democratic states. Its main goals and motives for action were to secure the power of the League of Communists of Yugoslavia (LCY) and to prevent the development of any political opposition that would threaten their rule. UDBA’s methods and ways of action have been analysed through a case study – Operational Action (operation) “Paromlin” and the fate of one of the involved persons (Vinko Marković) who suffered because of its implementation. Operation “Paromlin” was the code name for UDBA’s investigation of the explosion of a handmade device in Zagreb on September 17, 1975. There were no human casualties in the explosion and only minor material damage was caused. Considering that the explosion happened while Josip Broz Tito, President of the SFRY, was visiting Zagreb, and near a place where he had been the day before, it was interpreted as an assassination attempt. In addition to the hypothesis that it was an attempt at assassinating the President, which was propagated by some authors along with the UDBA, an even more intriguing hypothesis was that the whole case had been set up by the State Security Service. This hypothesis was advocated by persons who were convicted of planting the explosive device, but also by many others. This book is also an analysis of these two hypotheses. The main goal of the book is to show how the UDBA “operated”, i.e. how and by what methods the State Security Service proceeded against those who they considered as political opposition. This goal was pursued by exploring Operation “Paromlin” and by analysing the fate of an individual person (Vinko Marković). Marković was not a significant historical figure, but his life is an excellent template for analysing the activities of the UDBA and the entire repressive system of the SFRY. Marković was a low-rank member of the LCY, who was innocently accused of anti-state activities, brutally beaten during the investigation conducted by UDBA’s agents, and sentenced to eight years of strict imprisonment in Stara Gradiška. The book also shows UDBA’s treatment of political prisoners both during their sentence and after they were released. Various causes and reasons for these overly repressive actions have been suggested to explain the relationship between the State Security Service and the highest political levels in Yugoslavia. The activities of the Yugoslav repressive apparatus have been presented through the fate of an individual. Therefore, the case study has been combined with data on the principles and methods of work of the State Security Service, as well as data on the political context in which the whole case took place. In the chapter on “Investigation,” it is shown how Vinko Marković came under the scrutiny of the State Security Service, how and why an investigation was launched against him, and what the investigative process (UDBA’s “operational processing”) looked like. The book also reveals the identity of UDBA’s associates who ruined the lives of innocent people with their dishonourable actions, especially one of the agents who applied the most brutal torture against Marković and other suspects. The chapter “In the Court” traces the instrumentalised activities of the judiciary through the presentation of a mounted trial of the group convicted for the explosion in Paromlinska Street in Zagreb. A separate sub-chapter is devoted to the issue of terrorism and Croatian emigration. The chapter on “Prison” gives an overview of Marković’s life in prison and analyses how the Service continued to monitor him and other political prisoners even behind the prison bars. The gatherings of political prisoners and their activities in the Stara Gradiška prison are described, as well as the fates of the convicts after their release. The “Concluding Remarks” provide an answer to some historiographically unresolved questions, such as whether the entire trial for the explosion in Paromlinska Street was rigged by the State Security Service or why the political police acted that way. At the end of the book (“Appendices”), there are several facsimiles of original archival documents. The book is based on abundant archival material that has only recently become available to researchers. It is primarily the archival fund of the State Security Service of the Republican Secretariat of the Interior of the Socialist Republic of Croatia (fund no. 1561), which is kept in the Croatian State Archives in Zagreb (HDA). Several other funds from the same archives (HDA) were used: the archival fund of the Central Committee of the League of Communists of Croatia (f. no. 1220), the archival fund of the Service for the Execution of Criminal and Misdemeanour Sanctions of the Republican Secretariat of Justice and Administration of the Socialist Republic of Croatia (no. 1560), and the archival fund of the Vjesnik newspaper (f. no. 2031). Documents from the Archives of Yugoslavia (Belgrade) (archival fund of the League of Communists of Yugoslavia, no. 507), and Jakša Kušan’s (private) archive (Zagreb) were also used to a lesser extent. The private archive of Vinko Marković’s family (Vinkovci) was used extensively. Research for the book also included oral history, primarily the author’s conversations with some of the actors in this historical story (Jakša Kušan, Đuro Perica, Antun Zink, and the family of Vinko Marković).