More than 2000 nuclear test explosions were conducted between 1945 and 1996, the year when the Comprehensive Nuclear-Test-Ban Treaty was concluded. The Treaty bans all nuclear explosions on earth. The film depicts the activities of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization in establishing a global verification regine to monitor compliance with the Treaty. It presents the challenging work at some of the monitoring facilities and at the International Data Centre in Vienna, where the data generated by the facilities are received, processed and analysed