The epistolary heritage of two brilliant poets of the First Portuguese Modernism, Mário de Sá-Carneiro and Fernando Pessoa, is a valuable resource of historical and biographical information. The considered “literary” correspondence covers the period from 1912 to 1916. It reaches its intensity by 1913-1914, when Mário de Sá-Carneiro conceived new literary works as well as his own new aesthetic concept. The article attempts to distinguish from Mário de Sá-Carneiro’s letters to Fernand Pessoa potential fictions due to a detailed description of the plots of future works and the analysis of individual fragments, also given in the text of the letters.