This article analyzes a set of dispatches related to the business correspondence of the Spanish Ambassador, Juan Miguel Paez de la Cadena, in St. Petersburg. The article gives an archaeographic description of the historical source of research into the problems of the history of the revolt of 1825. It further shows the peculiarity of the life of the metropolitan information field immediately after the death of Emperor Alexander I. This approach to studying the main plots of the history of the interregnum enables to highlight major problems concerning the Russian society and to pay special attention to the Polish question in this case. An analysis of the messages of the second half of December-early January demonstrates, on the one hand, the prevalence in the Russian ruling circles of the mythologem about the all-European conspiracy of secret societies, and, on the other hand, the nature of its transformation in the midst of a deep political crisis in the Russian Empire. The article shows how this concept and which of its elements acquire a new dimension and are reflected in the rhetoric of the young emperor and his entourage, and above all, K. V. Nesselrode. It is related to the problem of a priori definition of the key organizers of the rebellion. According to the renewed discourse, this role was assigned to the Poles and representatives of the titled aristocracy. It was them who, relying on the Spanish experience, intended to involve soldiers by deceit, commit violent acts against the tsar's family and sow anarchy and disorder.