“Rappaccini’s Daughter” begins long ago, in the Italian city of Padua, where Giovanni Guasconti has recently moved to study medicine. His lack of money compels him to rent a room in a dilapidated manor that once housed an aristocratic family. Giovanni immediately notices a small garden outside his window and asks a local, Dame Lisabetta, whether it belongs to this house or the neighboring plot. Lisabetta informs him that an old doctor lives there and experiments with the many varieties of poisonous plants that he grows in the garden.
Just then, the old doctor, Giacomo Rappaccini, emerges, tending the plants with care. One especially beautiful shrub with purple flowers sits in the middle of a fountain. Rappaccini is so wary of its potency that he calls his daughter, Beatrice, and asks her to care for it from now on. Beatrice is a light-hearted and stunning young woman who embraces the shrub as her sister. Giovanni is perplexed—why should Beatrice be so at ease with the flowers when Rappaccini avoided their poison? He resolves to himself to approach the matter rationally.
Giovanni raises this question to a family friend and mentor, Professor Pietro Baglioni. Baglioni is the professional rival of Rappaccini and is displeased to hear his pupil taking an interest in Rappaccini. Baglioni claims that Rappaccini is a genius but cold-hearted—uninterested in humanity except insofar as experimenting on his patients gains scientific knowledge. Baglioni warns Giovanni to beware of any dealings with the Rappaccinis and privately vows to protect Giovanni using his medical knowledge.
Giovanni returns home to witness a strange sight—both Beatrice and the purple flowers seem to kill whatever living thing crosses their path. Giovanni also catches Beatrice’s eye that night and tosses her a bouquet he purchased on a whim. It seems to wilt in her hands. Giovanni ponders his recollection of the night for many days with increasing agitation.
Lisabetta offers to show Giovanni a path to the garden, fundamentally altering how he interacts with Beatrice. As soon as the two meet in the garden, Giovanni throws caution to the wind and courts Beatrice. She requests that he only evaluate her based on what she says, not what he sees of her. Giovanni consents. At the end of this encounter, Giovanni reaches to touch the purple flowers, but Beatrice yanks his hand away. Where she touched him, his wrist becomes bruised and aching for several days, further confirming that her body is poisonous.
As their romance progresses, Giovanni continues to scrutinize each encounter to determine whether Beatrice’s soul is pure or corrupt. He changes his mind moment-to-moment based on her mood and behavior, and his quandary quickly spirals into obsession. When he chances to meet Baglioni again, Baglioni reaffirms that Giovanni should beware. Rappaccini himself also passes by during that encounter, and both Baglioni and Giovanni agree that Rappaccini gave the young man a particularly searching look.
Days go by in a lovers’ haze for Giovanni before Baglioni pays him a visit in his room, noting that Giovanni’s room smells faintly of poisonous flowers. He then tells a story about how Alexander the Great was gifted a woman from India only to discover that her body was poisonous. Baglioni asserts that he has discovered Beatrice is the modern version of such a woman, made deadly by her father’s experiments, but he has secured an antidote from a colleague. Steering Giovanni’s course, Baglioni charges him to confront Beatrice and encourage her to drink it.
Giovanni leaves Baglioni to attend his regular meeting with Beatrice. On his way, he buys flowers for her, thinking that if they wilt in her hand, he will have proof that she is poisonous. However, gazing at his handsome body in a mirror, Giovanni discovers that his hands are wilting the flowers, implying that he himself has become poisonous. In a rage, he confronts Beatrice, furious that she has intentionally made him like her. Shocked, Beatrice insists that she never intended to harm him, only to love him for a little while. She says her father must have done it.
Giovanni hands her the antidote, explaining that it may restore them both to health. Rappaccini joins them, gazing at the two proudly. He explains that their poisonous bodies protect them from any harm mankind would wish to inflict. But Beatrice contends she would have preferred being loved than feared by her fellow man, and she drinks the potion. As she dies, she asks Giovanni whether he did not have more poison in his soul than she. Baglioni, who has been watching the scene from Giovanni’s window, cries out in triumph and horror, rebuking Rappaccini for creating a monster stranger than fiction in his attempt to interfere with Nature.