At a party, recent high school graduate Walter “Gib” Gibson unsuccessfully propositions several girls and complains to his friend, Lance, that he has lost his touch. Lance, who is heading to the University of California, Los Angeles (UCLA), consoles Gib that college girls are more willing to have sex, but warns that the intellectual girls at Gib’s East Coast, Ivy League school are uptight. Sometime later, Gib writes to Lance and reports that he has been ineffective at finding a mate. In an English class, Gib sits next to Alison Bradbury, who takes copious notes as Professor Taub returns a writing assignment. After chiding Gib about his whimsical yet sloppy essay about pizza consumption, Professor Taub tells Alison that her paper lacks personality and suggests that she lighten up. The eccentric professor declares that in order to write well, one must experience life to its fullest. Later, as Gib plays football, Alison walks by with a friend who comments that Gib is cute, but when Gib eyes Alison, his teammate says she will only go out with him out of pity because he is failing English. Inspired, Gib follows Alison to an indoor pool and asks her to be his tutor. Although Alison ignores him, Gib describes the destitute future that awaits him if he fails school, and falls into the water. Soaking wet, Gib waits for Alison and, after checking her appointment book, she agrees to tutor him that evening. As Gib gets ready, his roommate writes a vulgar love letter and advises Gib to proposition Alison with a sentimental declaration of love, but Gib thinks it clichéd. As students party on campus, Gib arrives at Alison’s quiet dorm room, where she is ending a phone call with her boyfriend, Jason, a law student at UCLA. Promising to visit Jason over winter vacation, Alison tells her boyfriend that she loves him. At the library, Alison reads Gib’s paper aloud with disdain and, despite her reluctance, she follows Gib through a prohibited entry to the roof. Gib impresses Alison with his knowledge of astronomy and she warms to him, but when Gib recites his roommate’s speech, she knocks him over in anger and runs away. On Monday morning, Gib apologizes and Alison forgives him. However, Gib accidentally hands his roommate’s raunchy love note to Professor Taub and when she reads it out loud, Alison is disgusted. Sometime later, Gib receives a call from Lance, who invites his friend to California for winter vacation. When Gib hesitates, Lance promises to set him up with a beautiful blonde, The Sure Thing, and explains that she never refuses sex. Racing to the campus “Ride Board,” Gib finds a lift to Los Angeles, but when he gets in the car, he discovers Alison has responded to the same post so she can visit Jason. On the road, driver Gary Cooper and his girlfriend, Mary Ann Webster, sing show tunes while Gib and Alison sit silently in the backseat and Gib fantasizes about The Sure Thing. Later, a passenger in a passing truck flashes his naked bottom at the car and although Gib thinks it hilarious, Alison is offended. When Gib says Alison is repressed and berates her for lacking spontaneity, she takes off her shirt and leans out the window, exposing herself to another passing vehicle. After Gary is pulled over by a police officer and cited for multiple offenses, he throws the students’ luggage on the road and speeds away. Refusing to hitchhike, Alison storms off and forbids Gib to follow. Sometime later, Alison crosses paths with Gib and hesitantly agrees to his offer of beer and fried pork rinds, but they argue and she accepts a ride with a pickup truck driver. When the man tries to take advantage of her, Gib appears from the bed of the truck and scares the driver away by pretending to be a psychopath. At a bus station, Gib discovers he doesn’t have enough money for a ticket to Los Angeles, but he gives a vagrant some cash. Although Alison loans Gib some money, it is not enough for a ticket, and after she heads for the bus alone, she surprises him by returning to the station. Checking into a motel, Gib instructs Alison about drinking beer. Alison breaks away from an intimate moment to call Jason and report she will be arriving in Los Angeles late as Gib storms away in jealousy. At a bar, Gib again fantasizes about The Sure Thing and spends his remaining cash on drinks for locals, who join him in the incantation of Christmas songs. The next morning, Gib rushes Alison to get on the road. After stuffing Alison’s shirt with scarves so she appears pregnant, they are offered a ride, but when they arrive at a restaurant, Alison realizes she left her appointment book and cash at the motel. That night, they are caught in a rainstorm, but Alison discovers her father’s credit card and they find lodging at a fancy hotel. As they eat dinner, Gib tells Alison about his fascination with outer space and, later, Alison invites him to share the bed. When Gib inquires about Jason, she tells him their plans for the future. That night, Gib dreams about Alison instead of The Sure Thing. In the morning, Alison is pleased to find herself in Gib’s arms, but Gib pulls away. Later, Gib and Alison hitchhike with a truck driver heading to Los Angeles. Thinking that Alison is asleep, Gib tells the driver about The Sure Thing, but Alison wakes up and overhears the conversation. When they arrive at UCLA, Alison storms away in anger, telling Gib to enjoy The Sure Thing. As Alison settles into Jason’s dorm room and surprises her boyfriend by requesting beer instead of tea, Gib reunites with Lance at a fraternity house party. Alison hears the party and wants to go, but Jason is averse to parties. Meanwhile, Lance dresses Gib in festive Hawaiian garb and when Gib complains, Lance reflects that his friend has become more conservative. Seeing The Sure Thing arrive at the party, Gib confesses to Lance that he cannot go through with his plans to have sex with her, but when he notices Alison and Jason in the crowd, he decides to pursue The Sure Thing after all. On the dance floor, Alison and Gib eye one another dispassionately and at the punchbowl, they argue about each other’s sleeping habits. As Alison stomps out of the party, Gib takes The Sure Thing to Lance’s room. Later, in bed, Alison swears she did not make love to Gib, but when Jason asks Alison if she loves Gib, she is silent. Back on the East Coast, Professor Taub reads Gib’s story, “The Sure Thing,” to the class and Alison learns that he did not sleep with the girl because he had learned the true meaning of love. Alison tells Gib that she broke up with Jason and, later that night, they kiss for the first time on the library roof, underneath the stars.