Nathalie is the name a Parisian prostitute assumes for a special mission or "private investigation." She is engaged for this unusual, and secretive task by a professional, upper middle class wife who fears her husband is unfaithful to her. Nathalie has to seduce the clueless husband and regularly report all details of her relationship with him, including his most intimate sexual preferences in bed. Nathalie is stunning, charming and cunning. Can Nathalie and her reports to the mistrustful wife be trusted? Is the middle aged husband indeed unfaithful?