Oliver Barrett IV, heir of an old money East Coast White Anglo-Saxon Protestant family, attends Harvard College where he plays ice hockey. He meets Jennifer "Jenny" Cavilleri, a quick-witted, working-class Radcliffe College student of classical music; they fall in love despite their differences. Oliver's father drives a long distance to Ithaca, New York, to see his son's hockey game vs. Cornell for the All-Ivy title. Barrett is suspended from the game for fighting and Harvard loses to Cornell, 4–3. Oliver turns down his father's offer of a steak dinner and help in getting into Harvard Law School.
Jenny reveals that she has a scholarship in Paris arranged for after her Radcliffe graduation. Oliver is upset that he does not figure in Jenny's plans and proposes marriage. She accepts his proposal and he takes her to the Barrett mansion to meet his parents, who are uncomfortable with her Italian-American and blue-collar background. Oliver's father says he will cut him off financially if he marries Jenny.
They visit her father, Phil, a widowed baker in Cranston, Rhode Island, who wants Oliver to get along with his father. Phil wants a Catholic wedding but Oliver and Jenny marry themselves with him reciting "Song of the Open Road" by Walt Whitman and her reciting "Sonnett 22" by Elizabeth Barrett Browning.
Jenny works as a teacher but without his father's financial support the couple struggles to pay Oliver's way through Harvard Law School. Oliver graduates third in his class and takes a position at a high-powered New York City law firm. They are ready to start a family but fail to conceive. After Jenny undergoes three blood tests, Oliver is told that she is terminally ill.
Oliver attempts to continue as normal without telling Jenny of her condition, but she confronts her doctor and finds out the truth. Oliver buys tickets to Paris, but she declines to go, wanting only to spend time with him. Oliver seeks money from his estranged father to pay for Jenny's medical care. His father asks if he has "gotten a girl in trouble". Oliver says yes, and his father writes a check.
From her hospital bed, Jenny makes arrangements with her father for a Catholic funeral. She tells Oliver to not blame himself, insisting that he never held her back from music and Paris and it was worth it for the love they shared. Jenny's last wish is for Oliver to embrace her tightly as she dies.
A grief-stricken Oliver leaves the hospital and he sees his father outside, who has rushed to New York City from Massachusetts to offer his help after learning about Jenny's condition. Oliver tells him, "Jenny's dead," and his father says "I'm sorry," to which Oliver responds, "Love – Love means never having to say you're sorry", something that Jenny had said to him earlier. Oliver walks alone to the open air ice rink, where Jenny had watched him skate the day she was hospitalized.
