'Sous le Masque' is a documentary that explores the vibrant celebration of Carnival in the Municipality of Saint-Josse-ten-Noode, Brussels, Belgium's most densely populated and multicultural neighborhood. The film delves into how the community, with its rich diversity, engages with this longstanding tradition. Central to the narrative is Jossé, who emerges as the embodiment of Carnival and the symbolic figure of Sint-Joost. The documentary examines the deeper meaning of Jossé’s role for the local residents and how they interact with and navigate the cultural significance of the event. It raises important questions about identity, tradition, and the way a multicultural society embraces its heritage in a modern, urban context.