The sign left by Delacroix in the Church of Saint-Sulpice, a sleeping beauty waiting somewhere to be saved, a demon guarding a cursed treasure, and 64 scattered stones... For the first time, the Avant-Propos is systematically analyzed, word by word, to discover many answers hidden behind its coded lines and to let the Serpent Rouge bring to the light a surprising story about a secret lost in the ancient past of Paris.