Lucy Harmon, a nineteen-year-old American, is the daughter of well-known (now deceased) poet and model, Sara Harmon. The film opens as Lucy arrives for a vacation at the
Tuscan villa of Sara's old friends, Ian and Diana Grayson (played by
Donal McCann and Cusack, respectively). Other guests include a prominent New York art gallery owner, an Italian advice columnist and an English writer, Alex Parrish (Irons), who is dying of an unspecified disease. Diana's daughter from a previous marriage, Miranda Fox (Weisz), is also there with her boyfriend, entertainment lawyer Richard Reed (
D. W. Moffett). Miranda's brother, Christopher (Fiennes), is supposed to be there, but he is off on a road trip with the Italian son of a neighboring villa, Niccoló Donati (Roberto Zibetti). Lucy was particularly excited to see Niccoló, whom she had met on a previous visit to the villa, four years earlier, and who was the first boy she'd ever kissed. Lucy and Niccoló had briefly exchanged letters after this first visit. One letter in particular Lucy had admired so much she memorized it.
Lucy reveals to the gallerist that she is there to have her portrait made by Ian, who is a sculptor. She says it's really just an excuse for her father to send her to Italy, "as a present." Smoking marijuana with Parrish, Lucy reveals that she is a virgin. When Parrish shares this information with the rest of the villa the next day, Lucy is furious and decides to cut her visit short. While she is on the telephone booking a flight to New York, however, Christopher and Niccoló return from their road trip, and Lucy is once again happy, although she is disappointed that Niccoló did not immediately recognize her.
That evening, Niccoló comes to the Grayson villa for dinner, accompanied by his brother, Osvaldo (Ignazio Oliva). After dinner, the young people separate from the adults to smoke marijuana. Lucy is now able to laugh about Parrish's betrayal, and the group take turns recounting when they each lost their virginity. When the question comes around to Osvaldo, he demurs, saying, "I don't know which is more ridiculous, this conversation or the silly political one going on over there [at the grown-ups' table]." Lucy fawns over Niccoló but abruptly vomits in his lap.
The next day Lucy rides a bicycle to the Donati villa, looking for Niccoló. A servant informs her that he is in the garden, where Lucy finds him kissing another girl. Hastily bicycling away from the compound, she passes Osvaldo, who has been hunting with his dog. As she passes, Osvaldo holds up a jackrabbit he has killed and cries, "Ciao, Lucy!" Lucy doesn't stop but loses control of the bicycle at the next turn. Osvaldo tries to help but Lucy rebuffs his efforts and rides on.
The next day, Lucy poses outdoors for Ian's sketch studies, at one point exposing one of her breasts. Niccoló and Osvaldo arrive in a car. Niccoló ogles Lucy, but Osvaldo looks away, decrying Lucy's lack of propriety. Ian dismisses Lucy, who wanders off into an adjacent olive grove, followed by Niccoló. They begin to make out, but Lucy eventually pushes him away.
Retreating to the guest house, Lucy shares her notebook with Parrish. Up to this point, the viewer has been led to believe that this notebook contains Lucy's writings. Now it is made clear that this is one of Sara Harmon's last notebooks. It contains an enigmatic poem that Lucy thinks holds clues to the identity of her real father. Throughout the film, she has been asking probing questions about her mother. Did Parrish ever know Sara to wear green sandals? Had Ian ever eaten grape leaves? Had Carlo Lisca (a war correspondent friend of the Grayson's whom Sara had known) ever killed a viper? All of these images are found in the poem, which Lucy now reads to Parrish. Lucy and Parrish agree that the poem must refer to Lucy's real father.
That evening, Lucy wears her mother's dress to the Donati's annual party. Almost immediately after arriving, Lucy sees Niccoló with another girl and the two do not speak. Lucy sees Osvaldo playing clarinet in the band that is providing musical entertainment. She later sees Osvaldo dancing with a girl, but they exchange earnest glances. Lucy picks up a young Englishman to take back to the Grayson's villa. On the way out, Osvaldo chases Lucy down and says that he's interested in visiting America and would like advice. They agree to meet the next day. Lucy leaves with the Englishman, who spends the night at the Grayson's villa but without having sex with Lucy.
The next day, Parrish's health takes a turn for the worse, and he is taken to the hospital. After the ambulance goes, Lucy skulks around Parrish's quarters in the guest house. Looking out one of his windows, she sees one of Ian's sculptures of a mother and child. The expression on her face suggests that she has had an epiphany. She goes to Ian's studio and asks him where he was in August 1975, when she was conceived. Ian says he was here, fixing up the villa. He says he thinks that might have been when Lucy's mother was at the villa, having her own portrait made. Lucy says, "That's what I thought." Ian says they could ask Diana, but then he remembers that Diana was back in London at the time, finalizing her divorce. Without explicitly saying so, the two appear to acknowledge that Ian is Lucy's biological father, and Lucy promises to keep the secret.
In the meantime, Osvaldo has arrived at the villa. When Lucy exits Ian's studio, she is stung by a bee. Osvaldo rescues her and takes her to a brook, giving her wet clay for her stings. As they walk through the countryside, Osvaldo confesses that he wrote to Lucy once, pretending to be Niccoló. This letter turns out to be the letter that Lucy loved above all the others, the letter which she memorized. Lucy can't believe it, but Osvaldo recites part of the letter and takes Lucy to a tree he had described in the letter as "my tree."
Lucy and Osvaldo spend the night under the tree, where Lucy finally loses her virginity. As they part the next morning, Osvaldo confesses that it was his first time too.
