This article presents an unpublished and largely unexplored source written in Basel during the international church council, the Vita fratrum predicatorum conventus Basiliensis (1442–1444). It deals with the reform of the Dominican friary, which was effectuated just before the start of the council to prevent scandals. Johannes of Mainz, its author, was the first lector of the reformed friary and wrote the text to corroborate the reformed religious identity of his community. He presented the reform of the Basel friary—which aroused fervent opposition of the original inhabitants—as a new episode in the history of salvation. A second part of the Vita fratrum eulogized the characteristics that Observant friars have in common. By “othering” Conventual friars and by depicting their horrible deaths, Johannes tried both to convince the Observant Basel friars of their superiority over Conventuals and to exhort them to stick to an Observant lifestyle. Unfaithful friars, the narrative warned, were eradicated from the celestial vineyard. For the last part of the Vita fratrum, which presents “the most fruitful plants” of the vineyard, Johannes of Mainz drew up personal and original biographies of contemporary Dominicans, such as Johannes Nider (d. 1438), who is presented as a “mirror of observance” and a “doctor of souls.”