This book describes the discovery of the murals painted by the group Alianza de Trabajadores de las Artes Plásticas (ATAP) in 1930 at the Carlos A. Carrillo School, hidden under several layers of paint. The point of origin was a folder of unidentified photographs, which are under the protection of the Francisco Xavier Clavigero Library at the Universidad Iberoamericana. After conducting research through books and magazines of the time, it was found that they were the murals of the Plutarco Elías Calles School, in Colonia Portales. The details of the research are described: the origin of the photographs, the context of the works with the socialist education project of that time, identification of each of the School's mural cycles. In addition, the latest news of the discovery is documented in the process of searching for the murals through openwork on the walls of the School and what appeared when the layers of paint were lifted. Included are some virtual reconstructions carried out by specialists and the 20 photographs found in the Library's folder.