When Milo Ames receives a troubling letter from his childhood nanny, Madame Nanette, he and Amory travel to Paris where they are soon embroiled in a mystery surrounding the death of a famous parfumier. The more Amory and Milo look into the motives of industry rivals and heirs who are vying for control of his perfume empire, the more they are convinced that Nanette may be right. When secrets unfold and things take a dangerous turn, Amory and Milo must work quickly to uncover the essence of the matter and catch a killer before the scent goes cold.