This Master thesis includes conservation and restoration work on a fragment of a detached wall painting made by the artist Osvaldo Bierti and later returning it in situ together with the remaining fragments. The wall painting was located on the vault of the church of the Blessed Virgin Mary in Jastrebarsko. Although a small town, Jastrebarsko has many cultural and historical monuments, including a Franciscan monastery with a church whose oldest parts date from the 16th century. In the central part of the curved sanctuary vault, on several older paint layers, there was a medallion from 1908. made by the mentioned master. To avoid damage during the static restoration of the vault, the medallion was detached in 2012 by the stacco method. It was separated into 5 fragments/parts, of which one was restored as a part of Dominik Marijić's Master thesis in 2016 and two as part of Benedikta Vilenica in 2018. The fragments were also prepared for connecting and retuning in situ. At the very beginning of the conservation and restoration work of the fragment,previously made research results were studied as well as used materials and methods applied on previously conserved and restored fragments, so that the procedures on the fragment D could be harmonized with others. The works included treatment of the backing, consolidation of the original plaster, reintegration of the intonaco plaster on the back of the fragment, laying of the intervention layer, making a new carrier, removal of facing, cleaning the image, and reintegration of the painted layer. After all the necessary interventions, a detailed plan for returning the fragments in situ was made. The fragments were adequately stored and transported to the church of the Blessed Virgin Mary, where they were returned to the vault, one by one, for easier handling and for monitoring the process of connecting them together. In situ, before mounting the individual fragment, the carrier was processed to allow the fragments' better fitment. The fragments were physically mounted with construction adhesive, which respected the principle of reversibility – enabling the subsequent removal of the fragments. At the end, the medallion was integrated into the rest of the painting, respecting the decorative elements surrounding the medallion.