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. Helios Belanger died suddenly, shortly before the release of his newest, highly anticipated perfume, and Madame Nanette, who works for the family, is convinced that her employer's death was not due to natural causes. The more Amory and Milo look into the motives of industry rivals and the Belanger 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.