In 1961 London, Jenny Mellor is a bright and beautiful 16-year-old schoolgirl who wishes to attend Oxford University. Her studies are controlled by her strict, overbearing father, Jack. After youth orchestra rehearsals, Jenny waits at a bus stop on the street under the rain when she meets David Goldman, a charming older man driving a Bristol 405. Telling her that he is a music lover and that he is worried about her cello getting wet, David convinces Jenny to put her cello in his car while she walks alongside. As the rain becomes stronger, Jenny asks David if she can sit inside his car. The two continue talking about music and, before being dropped off, Jenny confesses that she will be able to do whatever she wants when she reaches university, such as going to art galleries and watching French films, wishing for a life of culture and luxury. The next day, David leaves flowers on Jenny’s front porch, wishing her luck at her youth orchestra’s concert. Later, she sees him outside the cafe she and her friends were in and approaches him. After a little small talk, David then asks Jenny if she is free to go see a concert and have supper with him and his friends. She happily agrees and thanks him.
On the night of the concert, Jack disapproves of Jenny going while her much more lenient mother, Marjorie, tells him otherwise. David comes by to pick Jenny up and to talk to her parents, where he easily charms his way into convincing Jack that he take Jenny home later than her intended curfew. They arrive at the concert where Jenny meets David’s friends, Danny and Helen. Afterward, they go to dinner at a fancy restaurant, where they invite Jenny to an art auction. David picks up Jenny at school and goes to the auction, winning a bid for a painting by Edward Burne-Jones and going to Danny’s place afterwards. They talk about Oxford and they all agree to go and visit together the following weekend.
Jenny hears a commotion late one night and sees David drinking with her parents. He then uses the opportunity to ask them if he can take Jenny to Oxford, saying that he used to study there and would like to visit his old teacher, Clive Lewis, the author of The Chronicles of Narnia. Her parents are reluctant at first, but agree, seeing it as a good opportunity. At Oxford, Jenny discovers that David is a con man who makes money through a variety of shady practices. She is initially shocked but silences her misgivings as she succumbs to David’s charm. Back at her home, Jenny and David have their first kiss. Jenny then shows a signed copy of The Lion, the Witch and the Wardrobe to her parents, which David actually signed. Impressed by his connections and charisma, Jack and Marjorie approve of their romantic relationship.
On the night of Jenny’s 17th birthday, David arrives with presents and tells her parents that he intends to take her to Paris as a special birthday gift. Her father angrily disapproves, but later agrees after David talks to him. In Paris, the two dance, take photos, and Jenny eventually loses her virginity to David. Back in London, Jenny gives her favourite teacher, Miss Stubbs, Chanel perfume as a gift from her trip. However, Miss Stubbs refuses the gift, telling Jenny that she knows where it came from and is both concerned and disapproving of her relationship with David. They argue and have a falling-out. Later that night, David proposes marriage. Jenny accepts the proposal and, after an argument with the headmistress, decides to drop out of school and not apply to university.
While getting petrol on their way to dinner with her parents, Jenny rummages through the car’s glove compartment for a cigarette and discovers, through letters, that David is already married, revealing that he only dated Jenny to con her and her family. Shocked, Jenny tells David to take her and her parents back home. Jenny argues with David, telling him she gave up her education to be with him and that he will go and tell her parents the truth with her. She then goes inside her house, her father asking what happened. Jenny tells her parents that David is mustering up the courage before going inside to confront them. However, he drives off and is never seen again.
Jenny despairs, blaming Danny and Helen for not telling her the truth early on and blaming her parents for letting her throw her life away with an older man. Later that night, Jack apologizes to Jenny, admitting that he messed up and that he believed David could give her the life she wanted. Jenny then goes back to her school, requesting to repeat her last year and take her exams, but is refused re-admission. She then goes to Miss Stubbs, asking for help. She resumes her studies and is accepted at Oxford the following year.