Isola Vire, a modern forensic toxicologist, wakes inside the body of a frail, neglected noble girl from the old aristocratic realm of Auris. The original young lady has been slowly poisoned for years by her stepmother, elder half-sister and father, who view her as a worthless bargaining chip to trade for noble marriage alliances. Drawing on her expert knowledge of toxins, medical records and pathological analysis, Isola instantly identifies the chronic lethal poison hidden in her daily medicine, medicated pillows and incense—marking the start of her fight to escape the death trap woven by her own family.