A 40-year-old computer scientist, a great fan of the painter Eugène Delacroix, is found murdered in the toilets of the Louvre museum, after having admired at length his famous painting "Liberty leading the people". Simon, a teenager with extraordinary memory skills, witnessed the tragedy but did not see the murderer's face. In charge of the investigation with police captain Antoine Verlay, art historian Florence Chassagne learns that the painting so admired by the victim must be taken down and transported for an exhibition in Japan.