While he was preparing the edition of his epistolary corpus, Gerbert of Aurillac removed 28 compromising letters from his initial corpus. These letters, mostly written between 984 and 987 during the succession crises to the thrones of the German Empire and West Francia, illustrate Gerbert's and Adalbero of Reims's triple game in the political struggle bringing into conflict the Ottonians, the Carolingians and the Capetians. Moreover, those confidential letters constituted the framework of an epistolary network involved in political intrigues and in the redefinition of continental dynastic balances. By its content and the links it draws between Gerbert and his correspondents, Gerbert's epistolary corpus is a precious source about the starting point, the constitution, the organisation, the structure, the form and the strategies of an epistolary network during a major political crisis. The study of this corpus leads to a better understanding of the upheavals (withdrawals, mergers, definition of a new strategy...) and their impact on it as a response to the challenges of the crisis. Finally, the study reveals the fate of the epistolary network after the rise of a new dynasty.