Six plants run through six ancient cultures across this BBC series: the blue lotus in Egypt, the fly agaric mushroom in Siberia, Salvia divinorum among the Mazatec in Mexico, the opium poppy in Greece, Syrian rue in Iran, and datura in India. Each episode follows a single plant back to the rituals built around it, from healing ceremonies to religious rites, with ethnobotanist Michael Carmichael, Egyptologist Alan Lloyd, and pharmacologist Susan Duty of King's College London explaining what these substances actually do to the body and why particular societies treated them as sacred rather than simply intoxicating. The Mexico episode features Mazatec shamans describing how salvia induces the visions used in their healing practice, one of the few traditions in the series still practiced legally today. Greece's episode traces the opium poppy from medicine into abuse, a split the series returns to throughout: plants once central to ritual life are now mostly illegal, and the six case studies together ask what changed, the substances or the societies around them.